Dirty Frag: Universal Linux LPE

https://www.openwall.com/lists/oss-security/2026/05/07/8

by flipped • 3 months ago

819 330 3 months ago

Disclosure Timeline

2026-04-29: Submitted detailed information about the rxrpc vulnerability and a weaponized exploit that achieves root privileges on Ubuntu to security@kernel.org.

2026-04-29: Submitted the patch for the rxrpc vulnerability to the netdev mailing list. Information about this issue was published publicly.

2026-05-07: Submitted detailed information about the vulnerability and the exploit to the linux-distros mailing list. The embargo was set to 5 days, with an agreement that if a third party publishes the exploit on the internet during the embargo period, the Dirty Frag exploit would be published publicly.

2026-05-07: Detailed information and the exploit for the esp vulnerability were published publicly by an unrelated third party, breaking the embargo.

2026-05-07: After obtaining agreement from distribution maintainers to fully disclose Dirty Frag, the entire Dirty Frag document was published.

flumpcakes• 3 months ago

7 days from disclosure to publishing a how-to guide to get root to the entire planet doesn't scream "responsible" disclosure to me.

bawolff• 3 months ago

Its not the reporter's fault that other people broke the embargo.

firer5• 3 months ago

My immediate reaction was the same.

But this is very similar to Copy Fail, and I'm assuming there was an assumption that others might also discover this soon as well. Hence the urgency.

At least that's my charitable interpretation.

lofaszvanitt2• 3 months ago

WTF cares? Publish them without disclosure is the true way, otherwise noone would care about security and your data.

john_strinlai5• 3 months ago

"Because the embargo has now been broken, no patches or CVEs exist for these vulnerabilities."

link: https://github.com/V4bel/dirtyfrag

detailed writeup: https://github.com/V4bel/dirtyfrag/blob/master/assets/write-...

importantly:

"Copy Fail was the motivation for starting this research. In particular, xfrm-ESP Page-Cache Write in the Dirty Frag vulnerability chain shares the same sink as Copy Fail. However, it is triggered regardless of whether the algif_aead module is available. In other words, even on systems where the publicly known Copy Fail mitigation (algif_aead blacklist) is applied, your Linux is still vulnerable to Dirty Frag."

mitigation (i have not tested or verified!):

"Because the responsible disclosure schedule and the embargo have been broken, no patch exists for any distribution. Use the following command to remove the modules in which the vulnerabilities occur."

    sh -c "printf 'install esp4 /bin/false\ninstall esp6 /bin/false\ninstall rxrpc /bin/false\n' > /etc/modprobe.d/dirtyfrag.conf; rmmod esp4 esp6 rxrpc 2>/dev/null; true"

conversation around the mitigation suggests you need a reboot or run this after the above on already-exploited machines:

    sudo echo 3 > /prox/sys/vm/drop_caches

progval2• 3 months ago

"sudo" in "sudo echo 3 > /prox/sys/vm/drop_caches" does not do anything because only runs echo, not the write.

And if a machine is already exploited, it's too late to do just that. You need to rebuild the whole disk image because anything on it could be compromised.

john_strinlai5• 3 months ago

And if a machine is already exploited, it's too late to do just that. You need to rebuild the whole disk image because anything on it could be compromised.

this is more targeted at the people who run the PoC to see if their machine is vulnerable.

just transcribing some relevant stuff from https://github.com/V4bel/dirtyfrag/issues/1 so that people visiting this thread dont need to poke around a bunch of different places.

dundarious2• 3 months ago

You can't sudo echo and redirect from the non-sudo shell like that.

    echo 3 | sudo tee /proc/sys/vm/drop_caches

    sudo sh -c 'echo 3 > /proc/sys/vm/drop_caches'

Also fixed your typo in /proc...

john_strinlai5• 3 months ago

thanks. copy pasting from the github via my phone, and should have taken the extra few mins

throw0101c2• 3 months ago

Also try:

     sudo sysctl -w vm.drop_caches=3

wpollock• 3 months ago

Or more simply, use

   su -c 'echo 3 > /proc/sys/vm/drop_caches'

danudey4• 3 months ago

Just FYI, you can also mitigate it with `echo 1 > ...`; you don't need to drop everything, dropping `1` clears the page cache and that's enough.

Tested locally on Ubuntu 26.04:

1. Ran the exploit and got root

2. Configured the mitigations

3. Ran `su` again with no parameters and immediately got root again unprompted

4. Cleared the page cache

5. `su` asked for a password

sounds• 3 months ago

Is there any additional info on where it was "published publicly by an unrelated third party"? From the timeline in the writeup:

2026-05-07: Submitted detailed information about the vulnerability and the exploit to the linux-distros mailing list. The embargo was set to 5 days, with an agreement that if a third party publishes the exploit on the internet during the embargo period, the Dirty Frag exploit would be published publicly.
2026-05-07: Detailed information and the exploit for this vulnerability were published publicly by an unrelated third party, breaking the embargo.

Edit: nevermind, details are further down in the thread:

https://openwall.com/lists/oss-security/2026/05/07/12

And

https://news.ycombinator.com/item?id=48055863

alecco• 3 months ago

People are blaming the guy who wrote the exploit for breaking the embargo but it was actually broken in Linux by publishing a fix [1]:

on 2026-05-05 Steffen Klassert pushed f4c50a4034 to netdev/net.git with Cc: stable@vger.kernel.org.

Once a fix is out it's usual for researchers to race to make the first exploit out of it.

[1] https://afflicted.sh/blog/posts/copy-fail-2.html

Tiberium• 3 months ago

Do you think with modern LLMs in a few years projects like Linux will have all those low-hanging security bugs fixed? Are we witnessing a transition period, or will nothing change?

staticassertion9• 3 months ago

New vulns are introduced to Linux every day. Fuzzers trigger every single day on Linux. No, nothing will improve here from AI.

Muromec2• 3 months ago

There is a finite number of bugs and betters tools that find them mean there is less bugs in the code.

alex_duf• 3 months ago

there's an argument to be made that new code will be inspected before being merged and therefore the classes of bugs an LLM is likely to find will not be merged until it's fixed.

spartanatreyu• 3 months ago

LLMs don't matter, linux's codebase has been growing much faster than it can be secured so this is all inevitable.

Transitioning components to rust eliminates certain categories of bugs leaving the rest of the bugs to be dealt with.

We'd likely end up needing another language with stronger type and effect systems to eliminate more categories of bugs. Probably something which enforces linear types, capabilities, units of measure types, and effects.

And you'd have to update linux itself to switch to capabilities.

tetha• 3 months ago

Out of this dataset of 2-3 vulnerabilities, I'm noticing a pattern: All of those are in older and/or niche kernel modules. That raises two thoughts:

Maybe the more regularly used kernel code has a lot of low-hanging security topics shaken out of it already.

And second, I'm indeed wondering what a good path to minimize the loadable kernel code is on a system looks like. My container hosts for example have a fairly well defined set of requirements, and IPSec certainly is not in there. So why not block everything solely made to support IPSec? I'm sure there is more than that.

After all, the most reliable way to higher security is to do less things.

miduil3• 3 months ago

This again does not work under Android, at least in termux compiled with clang/gcc.

ronsor• 3 months ago

Android has a lot of hardening and sandboxing that desktop Linux doesn't (and won't for UX reasons).

miduil3• 3 months ago

Yes, it demonstrates that it's possible to harden well - at least for some cases. It appears depending on the environment hardened kernel / runtime environments are pretty much possible to have safeguards working today already.

__float2• 3 months ago

desktop Linux doesn't (and won't for UX reasons)

Can you elaborate?

croes4• 3 months ago

Android has other problems

https://durovscode.com/google-android-security-update-warnin...

pjmlp5• 3 months ago

Because Android is not Linux, as much as some pretend it is.

In fact, given the official public APIs, Google could replace the Linux kernel with a BSD, and userspace wouldn't notice, other than rooted devices, and the OEMs themselves baking their Android distro.

grosswait3• 3 months ago

It absolutely is Linux, and yes the JVM could absolutely run on something else. But it is Linux and you can run Linux binaries directly on it - that just isn’t how it is used by end users.

staticassertion9• 3 months ago

I assume because the rxrpc module is not loaded / provided and because unprivileged user namespaces are not allowed, which should be sufficient to mitigate. Curious if someone else has more details though.

jeroenhd• 3 months ago

The exploit as posted contains x86 shellcode, so you'd need to drop in the appropriate shellcode to test if it really works.

Android wasn't vulnerable the last time, so far it's been a shining beacon of hope for proper SELinux configuration that I wish was more widely available in other places.

BadBadJellyBean• 3 months ago

Well this is getting tiresome. I wish there was a less stressful way to get fixes for such bugs. But the cat is out of the bag now.

Not criticizing whoever found the bug, of course.

unethical_ban2• 3 months ago

Here's a general question, are these vulnerabilities hitting Linux more than BSDs due to hit being a larger target or because its architecture is less secure by design?

staticassertion9• 3 months ago

Larger target.

golem14• 3 months ago

in many ways:

- more people are using it (assuming macos is in its own bucket perhaps) - bigger surface areas (esp NetBSD has in my limited understanding just less stuff that can go boom) - more churn, ie more new stuff than can be buggy released more often.

Of course, because of that, more eyes are on Linux, so I'm not sure where that security tradeoff is.

ahartmetz7• 3 months ago

AFAIU, Linux and the BSDs have basically the same architecture - the BSDs just value secure and simple, understandable code more highly than Linux vs features and performance.

angry_octet6• 3 months ago

This is really not a correct statement beyond the fact that both are a type of Unix.

rafram• 2 months ago

https://news.ycombinator.com/item?id=48077971

vsgherzi• 3 months ago

It’s two things. 1. Less eyes are on the bsds

2. Bsds don’t have the same optimizations that Linux has. Bsds generally try to pursue corrrectness

That being said there were just a bunch of vulnerabilities in freebsd

macOS has had its own dirty cow attack and I know there’s for sure more memory ones just based on the way the xnu kernel works.

So no Linux isn’t really worse per say

int0x29• 3 months ago

I'm curious what broke the embargo. Did it leak or did a third party find it independently?

john_strinlai5• 3 months ago

it was published publicly by an unrelated third party

jacobgkau• 3 months ago

They're asking the nature of the third party's discovery/publishing. Someone on the inside who decided to leak it anonymously? Someone else who was able to access some private communication they shouldn't have been able to see? Or a third party who happened to discover the same vulnerability (which seems less unlikely than normal since this is so similar to Copy Fail), but didn't follow disclosure procedures?

either-orr• 3 months ago

A link to the patch was posted in someone's X account. Someone else saw that and posted a working exploit in less than an hour (potentially exploited by an LLM, though other than the quick turnaround, claim not substantiated).

https://x.com/encrypted_past/status/2052409822998392962

reisse• 3 months ago

No embargo exists (or could possibly exist) in the first place.

Linux is open source, so every patch fixing the security bug is immediately visible to everyone. There is no workaround to that by the very design how the kernel is developed. The "embargo" people talking about is the rather stupid notion that if people keep their mouth shut and not write "THIS IS A LPE" straight in the patch description, everyone can pretend vulnerability is not leaked until the "official" message in the mailing list is sent.

This approach might have been defensible before, but in LLM era, when people have automated pipelines feeding diffs straight from the mailing lists to SotA models asking to identify probable security issues fixed by those, it is both stupid and dangerous.

zbentley4• 3 months ago

My (novice) understanding is that embargoes are intended to provide time to 1) develop a patch and 2) distribute the patch.

For Linux/public open source, what you said is right about 2). Once the patch is visible to anyone, it's trivial to identify exploits for unpatched systems. But 1) is still a valid use-case for embargoes for Linux vulns, right? Like, if this patch had taken a few weeks to develop before being confirmed working and published, that's potentially valid grounds for not sharing details during that time (within reason), no?

bjackman2• 3 months ago

Linux does actually have a proper embargo process. But, you're correct that in this case it wouldn't usually have been followed anyway. Bugs like this are fixed multiple times a week, anyone with basic kernel knowledge can see that they are potentially LPEs.

Usually, nobody even bothers to check. LPEs like this are too common to even categorise effectively.

account422• 3 months ago

The linked announcement specifically mentions that an embargo has been broken.

ajross• 3 months ago

It seems like the embargo bit is a bit spun. The exploit is a reasonable extension of ideas from Copy Fail and was independently discovered in public (on X, it seems like) before Kim's "embargo" had expired. No one broke any trust, the independent discoverer just didn't follow as rigorous a process.

oncallthrow2• 3 months ago

can this also be used to obtain container escape ?

synack• 3 months ago

If your container has setuid binaries and these modules are loaded, yes.

lights0123• 3 months ago

With the exploits published as-is, you'll only get root inside the container: there's no explicit namespace break, and calling setuid() in a container just gives you root in the container.

However, it can be used to modify files that are passed into the container (e.g. Docker run -v), or files that are shared with other containers (e.g. other Docker containers sharing the same layers). kube-proxy with Kubernetes happens to share a trusted binary with containers by default, which is how it can be exploited: https://github.com/Percivalll/Copy-Fail-CVE-2026-31431-Kuber...

miduil3• 3 months ago

It's poisoning the filesystem cache, if you don't have a setuid binary handy you just poison anything else that gets executed by the host.

awoimbee• 3 months ago

And your containers need to have specific capabilities enabled, which aren't by default on kubernetes and podman.

aaronmdjones• 3 months ago

You don't need any setuid binaries. You could just as easily use the vulnerability to add a job to crontab(5) that causes the cron daemon to run whatever you want as root.

firer5• 3 months ago

This is very similar in root cause and exploitation to Copy Fail.

Which illustrates pretty well something that's lost when relying heavily on LLMs to do work for you: exploration.

I find that doing vulnerability research using AI really hinders my creativity. When your workflow consists of asking questions and getting answers immediately, you don't get to see what's nearby. It's like a genie - you get exactly what you asked for and nothing more.

The researcher who discovered Copy Fail relied heavily on AI after noticing something fishy. If he had to manually wade through lots of code by himself, he would have many more chances to spot these twin bugs.

At the same time, I'm pretty sure that by using slightly less directed prompting, a frontier LLM would found these bugs for him too.

It's a very unusual case of negative synergy, where working together hurt performance.

eqvinox13• 3 months ago

No, unless I'm misreading it it's the *same* root cause: high 32 bits of Extended ESN in IPsec == authencesn module/cipher mode.

The wrong thing got fixed for copy.fail, because people jumped to blame AF_ALG.

[ed.: yes it's the same authencesn issue. https://github.com/V4bel/dirtyfrag/blob/892d9a31d391b7f0fccb... it doesn't say authencesn in the code, only in a comment, but nonetheless, same issue.]

[ed.2: the RxRPC issue is separate, this is about the ESP one]

firer5• 3 months ago

There are two vulnerabilities here.

The RxRPC one is definitely a different root cause (although caused by a very similar mistake).

For the ESP one it's a bit harder to tell. I don't think the wrong thing was fixed, just that there was a very similar bug in almost the same spot. Could be wrong about that though.

pepa652• 2 months ago

But if dirtyfrag is mitigated, copyfail is still active...

formerly_proven2• 3 months ago

These are all page cache poisoning attacks (dirtyfrag, copyfail, dirtypipe). Maybe the page cache should have defense-in-depth measures for SUID binaries?

firer5• 3 months ago

SUID mitigations have nothing to do with the vulnerability itself - just the exploit.

If there's a root cronjob that runs a world readable binary, you could modify it in the page cache and exploit it that way.

Modifying the page cache is a really strong primitive with countless ways to exploit it.

tptacek8• 3 months ago

I don't follow. LLMs spotted these bugs in the first place. You seem to be saying that these discoveries are indications that they're bad for vulnerability discovery.

firer5• 3 months ago

From what I understand, the copy fail bug was found by researcher who noticed something weird and then using AI to scan the codebase for instances where that becomes a problem.

I bet that with a slightly looser prompt/harness, the LLM could have found these twin bugs too.

Yet at the same time, I also think that if the human researcher had manually scanned the code, he'd have noticed these bugs too.

FWIW I do think LLMs are great tools for finding vulnerabilities in general. Just that they were visibly not optimally applied in this case.

eqvinox13• 3 months ago

I don't think the copy.fail people understood the issue they found, as is evident by the heavy focus on AF_ALG/aead_algif, which is essentially "innocent" as we're seeing here.

I think LLMs are great for vulnerability discovery, but you need to not skimp on the legwork and understanding what even you just found there.

parliament32• 3 months ago

No, they did not. Careful of falling for the psychosis.

This finding was AI-assisted, but began with an insight from Theori researcher Taeyang Lee, who was studying how the Linux crypto subsystem interacts with page-cache-backed data.

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

ofjcihen2• 3 months ago

I don’t think that’s what the OP is saying at all, just that using LLMs needs to be a cooperative research process.

Also I see you jumping around a lot to the defense of LLMs when I don’t think anyone is really attacking them. Maybe cool it a bit.

rayiner• 3 months ago

It’s incredible humans spot stuff like this. I guess even more incredible that LLMs can do it!

keybored• 3 months ago

Right. Finding the bug is in itself a win. It seems we’re jumping from that spend-electricity-to-find-bugs win to arguing about how some things around it are not quite good or comfy.

papascrubs• 3 months ago

Or a follow up prompt: "find similar classes of bugs". Once the actual case has been layed out finding like bugs isn't too hard. I hear you on the creativity bit. Like any tool, AI can put blinders on. Using it to augment without it fully taking over your workflow is tough.

dgellow2• 3 months ago

Not just like any tool though. Interacting with agents can be incredibly boring and frustrating in a way that I personally do not experience with other technology

varispeed• 3 months ago

When your workflow consists of asking questions and getting answers immediately, you don't get to see what's nearby.

That's why is very very important to just step out and use saved time to go for a walk, to a park, sit on a bench, listen do birds, close eyes and zoom out.

The state we are in is actually brilliant.

refulgentis• 3 months ago

It’s very hard to see a root vuln similar to, but not the same as, another discovered by AI, as a lesson about AI not exploring.

Is there a counterfactual where you would say it explored well enough, besides both vulnerabilities published as one?

SubiculumCode• 3 months ago

Evidence or are you just riffing?

timcobb3• 3 months ago

When your workflow consists of asking questions and getting answers immediately, you don't get to see what's nearby.

Very much aligns with my experience. For me this is the most unsatisfying thing about AI-based workflows in general, they miss stuff humans would never miss.

All the time I wonder what am I missing that's right nearby? It's remarkable how many times I have to ask Claude code to fully ingest something before it actually puts it into context. It always tries to laser through to target it's looking for, which is often not what you want it to look for, at least not all you want it to look for. Getting these models to open up their field of vision is tough.

ulrikrasmussen• 3 months ago

Do you think this is inherent or an artifact of prompting? Curiosity and side quests leads to higher token usage and longer time to finish, so I could understand why current harnesses and system prompts would not encourage that sort of thing.

But what if a coding agent was prompted to be more curious during development? Like a human developer, make mental notes of alternatives to try out and chase suspicious looking code which may seem unrelated to the task at hand. It could even spawn rabbit hole agents in parallel.

Taking a step back, this probably highlights major hazard with the increased usage of LLMs for coding, which is that everyone's style of work is going to converge because most code will be written by the 2-3 most popular models using the same system prompts.

dotancohen• 3 months ago

  > All the time I wonder what am I missing that's right nearby?

Add to the prompt "use coding conventions of the file which you are currently editing". That gets the machine (Opus and Sonnet at least) to go over the nearby code and occasionally mention something obvious.

clbrmbr• 3 months ago

It’s interesting to compare how the agentic search performs, with these targeted reads and lots of tool calls in the stream, versus the older but still valid paradigm of using a high-reasoning model like GPT-X-pro and feeding in all the relevant files at once with no tools.

I have found that the “pro” approach is much more holistic and able to tackle rather “creative” problems that require very careful design and the overall artifact is tight and self-consistent. — Claude Code by comparison is incredible in exploration and targeted implementation but indeed is not great at seeing the forest.

VladVladikoff2• 3 months ago

Actually lately I’ve been feeling the other way around with it. The LLM catches things I would have overlooked. I ask for a new feature in a certain file, and the LLM suggests fixing a tangentially related file to accommodate the new feature without breaking something else. Maybe this is just the crap legacy codebase I’m working with and how tangled up everything is, but I definitely have found several times now that it caught things I would have missed.

riedel• 3 months ago

Just on a side note. Negative synergy does not seem so uncommon with machine learning. We did some research maybe 10 yrs ago an human/ML based duplicate detection (for a municipal support ticket system) . Research showed that pure AI and pur human outperformed co-working. Human oversight often e.g. overcorrected machine work. I think it is a nice HCI problem to solve actually to amplify creativity and unique skills in such processes. Particularly if they can be to some degree repetitive and tiresome.

harshreality• 3 months ago

I don't know... after they found a high profile bug like copyfail, I wouldn't attribute not looking for similar bugs to them being overly dependent on AI. It's easy to stop exploring, for a while at least, after you've struck on a major find. Maybe they would've returned to it in a few months. It certainly inspired others to explore similar areas and find these new bugs. Isn't that enough?

totallyrandom__2• 3 months ago

Where does it say that the Dirty Frag one was found by LLMs? The research site with all the information doesn't mention LLM or AI at all.

zimbatm• 3 months ago

Maybe. This phenomenon of security holes being found closely to each other was also common before LLMs. People attention gets directed to a place and typically more issues are getting found.

YmiYugy• 3 months ago

AI or not, it’s always been reasonable common that a bunch of related vulnerabilities get discovered after shortly after the original one.

normie3000• 3 months ago

So umm... should I rush home and turn off all my computers?

arcfour3• 3 months ago

Are they already vulnerable to RCE as an unprivileged user? Hopefully not.

An LPE only allows an attacker who can already execute code on the system to become root. So, bad, yes, but it doesn't mean you are immediately pwned.

hughw2• 3 months ago

Should I rush to Lambda or ECS and turn off all my containers sharing a host with who the hell knows?

account422• 3 months ago

And for a single user desktop, an LPE is almost meaningless as all the really important files are in $HOME and accessible without root.

dezgeg• 3 months ago

For home computers, essentially https://xkcd.com/1200/ applies.

eqvinox13• 3 months ago

And I ask again: why the f*ck is algif_aead getting all the flak for copy.fail? It's authencesn being stupid.

authencesn didn't get fixed. Now we got the results of that, turns out you can access the same (I believe) out of bounds write through plain network sockets.

I wish I thought of that, but I didn't.

[ed.: I'm referring to the through-ESP issue. The RxRPC one is AIUI completely unrelated.]

xxpor3• 3 months ago

Linux is a single user system and should be treated as such. Run your services as root. Don't rely on unix user primitives for security.

wolttam2• 3 months ago

Running as root opens you up to a class of vulnerabilities (denial of service, mainly) that you can avoid by not running as root.

That said, running every process in its own micro VM is looking more attractive by the minute.

xxpor3• 3 months ago

Half the point is that you should always assume that there exists a complete LPE bug.

But yes, micro VMs are a great idea!

amarant• 3 months ago

Everything in this comment is wrong.

xxpor3• 3 months ago

Technically yes. Practically, I disagree.

256_• 3 months ago

I agree with the general sentiment. I treat anything running arbitrary machine code as if it has full access to a machine. I don't know where you get "run your services as root" from that, though. The principle of least privilege doesn't just apply to running malicious code, but running buggy code whose attack surface is exposed to evil-doers.

Sohcahtoa822• 3 months ago

This carries the same energy as "People will break into your car no matter what, so just leave your doors unlocked."

tptacek8• 3 months ago

The energy here is "so don't leave anything valuable in your car".

bigbuppo• 3 months ago

You say that, but I know someone whose house had their front door kicked in by burglars even though it wasn't even locked.

yencabulator2• 2 months ago

This actually happened to me. The seats had moved and glovebox was open one morning. Then a second break-in a few days later, and this one damaged the door panel near the lock. I left the doors unlocked for a couple of weeks after, to decrease the break-in damage -- there was never anything of value in the vehicle.

fragmede• 3 months ago

https://xkcd.com/1200/

zepearl2• 3 months ago

So if I understand correctly 3 modules are involved:

- esp4 (kernel config "CONFIG_AF_RXRPC")

- esp6 (kernel config "CONFIG_INET_ESP")

- rxrpc (kernel config "CONFIG_INET6_ESP")

Is this correct?

eqvinox13• 3 months ago

You mixed up the names vs. config options but yes killing those 3 options should make you "safe". No warranty.

zepearl2• 3 months ago

damn you're right, thx

arian_• 3 months ago

Every time someone finds a universal Linux privilege escalation, somewhere a sysadmin whispers 'this is why we don't run as root' while nervously checking if their containers are actually isolated.

oncallthrow2• 3 months ago

this is why we don't run as root

The entire point is that you can escalate to root

minimaltom2• 3 months ago

This attack class lets you escalate from any user to UID 0. Not running as root won't save you, in fact, this attack is for those processes not running as root.

However, if you are in a user namespace where UID 0 doesn't map to system-wide capabilities, and you dont share page cache for the setuid binaries on the system, this attack doesn't lead to LPE.

delamon3• 3 months ago

setuid binaries are not the only way to get root. E.g. one can change /etc/crontab or /etc/passwd. Or add trojan to /bin/ls and wait until admin type 'ls'

KamiNuvini• 3 months ago

Does anyone know whether Debian is vulnerable? I tried the exploit on a Debian 12+Debian 13 machine but wasn't able to reproduce it myself.

cholmon• 3 months ago

I just tried the exploit on a fresh Debian 13 droplet on digitalocean and it worked.

thaniri• 3 months ago

I was able to reproduce this issue on kernel 6.12.57+deb13-amd64 running Debian 13 (Trixie), but unable to reproduce it on kernel 6.1.0-42-amd64 running Debian 12 (Bookworm).

For anyone not on the security stream of Debian packages for Bookworm, kernel version 6.1.0-42-amd64 is actually immune to copy.fail. Surprising that it looks to be immune to dirtyfrag. If you haven't already patched on the security stream, you can choose any kernel version that kept commit 2b8bbc64b5c2. I am thinking that the same commit might accidentally be keeping certain Debian 12 kernel versions safe from dirtyfrag as well.

louwrentius• 3 months ago

I tested on a fully up-to-date Debian 13 and the exploit works. The mitigation also works / confirmed.

Existing4190• 3 months ago

https://security-tracker.debian.org/tracker/CVE-2026-43500

https://security-tracker.debian.org/tracker/CVE-2026-43284

baggy_trough3• 3 months ago

Debian 13 is offering linux-image-6.12.86+deb13 now.

chromacity3• 3 months ago

If this indeed works on all major distributions, I just continue to be amazed by how irresponsible the maintainers are. We're talking about optional kernel functionality that's presumably useful to something like <0.1% of their userbase, but is enabled by default?... why?

This feels like the practice of Linux distros back in 1999 when they'd ship default installs with dozens of network services exposed to the internet. Except it's not 1999 anymore.

TacticalCoder2• 3 months ago

... but is enabled by default?... why?

We could also wonder why XZ was linked to SSH... But only on systemd-enabled distros (which is a lot of them).

Just... Why?

And then make sure to call to incompetence, instead of malice and say non-sense like "Sure, it only factually affects systemd distros, but this is totally not related to systemd". All I saw though was a systemd backdoor (sorry, exploit).

Now regarding copy.fail that just happened: not all maintainers are irresponsible. And some have, rightfully, bragged that the security measures they preemptively took in their distros made them non vulnerable.

But yup I agree it's madness. Just why. And Ubuntu is a really bad offender: it's as if they did a "yes | .." pipe to configure every single modules as an include directly in the kernel.

"We take security seriously, look we've got the IPsec backdoor (sorry, exploit) modules directly in the kernel". "There's 'sec' in 'IPsec', so we're backdoored (sorry, secure)".

chuckadams• 3 months ago

xz was not directly linked to ssh, and systemd itself was not providing the backdoor. The weakness is embedded into the architecture of glibc (which has spread to other systems like FreeBSD as well): https://github.com/robertdfrench/ifuncd-up

akerl_4• 3 months ago

It’s not enabled by default. It’s an optional module that is loaded on demand. The entire setup of the kernel promotes compiling in the core set of things your users will need and offering basically everything else as a module to load on demand.

chromacity3• 3 months ago

This is a pedantry for the sake of it. If it's present by default and an attacker can trivially cause it to be loaded, it's the same as "on by default".

JeremyNT2• 3 months ago

Distro maintainers blacklisting specific functionality because they believe YAGNI is a pretty big ask. They just don't know who is using what. It's always possible for users to go back and tailor their builds for the stuff they actually want.

And... I remember the early days of Linux where I ran `make menuconfig` and selected exactly the functionality I wanted in my kernel. I'd... rather not end up back there.

That said a target for an easy win here is RHEL, which compiles a lot of modules into the kernel rather than leaving them as loadable modules, so the mitigation for e.g. copy fail was impossible. Maybe they could do with a few less of those?

chromacity3• 3 months ago

You can make precisely the same argument for network services. Who knows, maybe you need telnet and UUCP and NFS and ftpd running on your system?... why should the distro maintainer decide?

Well, because you probably don't, and it's a security risk, so no need to put millions at risk for the benefit of that one person who wants to tinker with packet radio or whatever. Similarly, it would be prudent for distros to not allow autoloading of modules that are extremely niche while giving a simple way to adjust the settings if you want to. God knows they have plenty of GUI configurators and config files already.

atgreen3• 3 months ago

Don't disagree, but there are eBPF mitigations that work as alternatives to unloading kernel modules.

michaelt• 3 months ago

Now I think about it, it's kinda weird if non-root users can cause kernel modules to get loaded, without any hardware changes having happened.

If the kernel modules for esp4, esp6 and rxrpc aren't loaded - how is it that a non-root attacker can cause them to get loaded?

TZubiri2• 3 months ago

Distro maintainers blacklisting specific functionality because they believe YAGNI is a pretty big ask

We have forgotten what a distro is, and its modern corruption of the concept is now taken as the definition.

Distributions weren't meant to be competing generic universal bundles of userspace tools in addition to the kernel.

ActorNightly3• 3 months ago

Because in order to exploit this, you have to have direct access to the computer. Either through malicious usb device, or by exploiting some supply chain or a known piece of software that will be willingly or automatically installed, and furthermore you need to be able to essentially run arbitrary terminal commands, which is a huge breach of isolation in that software.

If an attacker manages to do all that, its already bad news for you. Escalation to root with this is the least of your worries at that point.

Like someone else below posted, https://xkcd.com/1200/

People need to understand what the vulnerability actually is before freaking out about it.

cluckindan5• 3 months ago

So a threat actor buys access to a managed kubernetes service, or other linux-based shared hosting platform, and now they have access to the computer.

Hell, GitHub Actions would do.

netheril962• 3 months ago

You are assuming that LPE only applies to the user that holds all the sensitive stuff. But it also applies to users created specifically for isolation. Without LPE they would not have access to anything important even if they were compromised.

lunar_rover2• 3 months ago

In many ways non mobile computers are very much still stuck in 1999. Android is significantly more secure than other Linux systems because it's much younger and had the chance to integrate mandatory access control into the entire stack.

croes4• 3 months ago

Unless your Android doesn’t get any security updates anymore.

https://durovscode.com/google-android-security-update-warnin...

Atlas26• 2 months ago

The only thing Android shares with Linux desktop/server Linux is the kernel, the entire rest of the OS built on top of it is completely different so it’s a pointless comparison. While it uses the Linux kernel, it’s not considered the Linux everyone is commonly talking about here ie gnu/Linux (insert copypasta here).

Mobile OS are also essentially required to be much more controlled and locked down due to FCC regulations and the strictness surrounding modems and other RF emitting devices.

0xbadcafebee• 3 months ago

There is no way to disable components you think users won't use and not make it incredibly difficult to use the system. I personally would have no way to know what to enable or not enable based on what I want to do, and I've been using this stupid OS for 25 years.

Linux distro maintainers are the most responsible software maintainers on the planet. Their security practices are miles beyond the stupid programming language package managers, they maintain a select list of packages, vet changes, patch bugs, resolve complex packaging issues, backport fixes, use tiered releases, distribute files to global mirrors, and cryptographically validate all files. And might I remind you, they do all this for free.

nirui• 3 months ago

irresponsible the maintainers are

Today it's 0.1%, tomorrow it might become 100%. User demand is hard to anticipate, so it's reasonable to include small features that don't cost a lot to run by default.

It's not ideal, but you really don't want to prevent user from finishing their task, because maybe then they'll just give you a bad name and switch to another distro.

That's to say, it's not "irresponsible", it's reasonably maximums (at least trying to be).

kro2• 3 months ago

Maybe it would be reasonable for sysadmins to proactively whitelist used / block all exotic unused modules that are not needed in their system configuration.

This would reduce the amount of ring 0 code. But I've never seen such advice.

eqvinox13• 3 months ago

If you don't need it (rootless containers), you can disable unprivileged userns to block these two:

  echo 1 | sudo tee /proc/sys/kernel/apparmor_restrict_unprivileged_userns

May also break sandboxes (e.g. browser) though.

acedTrex• 3 months ago

Here we go again

jcims• 3 months ago

Tested Amazon Linux 2023 and it doesn't appear to be vulnerable in the default configuration. Would be interested if anyone finds anything different.

teaearlgraycold• 3 months ago

Anyone here with experience providing multi-tenant Linux systems (CI and the like), do providers usually disable kernel modules they don’t need to eliminate attack surface? Every time one of these comes out I wonder if I should be rotating every key in my GitHub CI or PaaS host. So far I haven’t seen any reports from the providers I use that they were pwned by any of these exploits.

TheDong• 3 months ago

A lot of these multi-tenant CI systems actually run everything in microVMs even if they present it to you as a container.

At this point, a microvm can be booted in ~200ms so you don't even have to keep a warm pool, you can just launch em on demand.

GitHub CI (actions) uses virtual machines.

kinow• 3 months ago

Just got an email from one HPC I have access in Germany. I guess all HPCs ans services like GH Actions are going to be offline for a bit. I think last time was on a Friday too, so it might be another Friday to organize emails, files, rotate backup/passwords...

hughw2• 3 months ago

Ran as a fresh new default user in a ubuntu:latest container

  git clone https://github.com/V4bel/dirtyfrag.git && cd dirtyfrag && gcc -O0 -Wall -o exp exp.c -lutil && ./exp

Result:

  dirtyfrag: failed (rc=3)

Good news!

Havoc• 3 months ago

Wouldn't count on container being a reliable testing platform for this. Loads of stuff - legitimate or otherwise - fails in containers

stsewd• 3 months ago

I got the same running it inside a container, but got a shell when running it directly in the host. This only shows that the exploit doesn't work inside a container. So, containers aren't vulnerable, or the script needs some adjustments to make it work in containers.

Since copy fail can be used to escape containers (https://github.com/Percivalll/Copy-Fail-CVE-2026-31431-Kuber...), I'm guessing the exploit needs some changes only.

cyphar3• 3 months ago

The repo you linked works by replacing files that are being used by other privileged containers on the same system. That works for the Kubernetes case (I'm a little surprised they don't use static binaries for their own privileged containers, seems a little dangerous to share any kind of data with untrusted tenants even if it's read-only) but not standalone containers.

However, there is a much an easier way of doing a breakout -- you can corrupt the host runc binary in a way analogous to CVE-2019-5736. The next time a container is spawned, the host runc binary will get run as as root and that's that.

Ironically, the first version of the protection against this attack I wrote also protected against page cache poisoning (by making a temporary copy of the runc binary during container setup in a sealed memfd and re-execing that) but the runtime cost of copying a 10MB binary at container startup was seen as too expensive by some users[1] so we ended up with a setup that shares the same page cache. I also distinctly remember arguing at the time that something like Dirty Cow could always happen in the future, and the memfd approach was better for that reason -- maybe I should've stuck to my guns more... :/

In practice the solution for containers is to update your seccomp policy to block the vulnerable syscall.

[1] https://github.com/opencontainers/runc/issues/1980

x4132• 3 months ago

this is why you don't contact distro mailing list. responsible disclosure is dead.

zbentley4• 3 months ago

At present it looks to me like the embargo was broken by someone identifying the patch as fixing a vulnerability, not someone leaking the mailing list.

More information may come out, or I might be missing something, but assuming that the above is accurate, this isn't a problem with responsible disclosure or mailing list opsec; it's a problem with the nature of open source. Right? Or are folks seriously proposing that the patch/mitigations should have been circulated to distro maintainers privately before going to mainline?

collinmanderson• 3 months ago

Or are folks seriously proposing that the patch/mitigations should have been circulated to distro maintainers privately before going to mainline?

I always assumed that distro maintainers got early access to patches before going mainline but maybe that’s not true?

73737373732• 3 months ago

Tanenbaum was right

TZubiri2• 3 months ago

Go on...

73737373732• 3 months ago

https://youtube.com/watch?v=oS4UWgHtRDw

Retr0id2• 3 months ago

Testing the rxrpc vuln on aarch64, I get a kernel data abort, which is interesting. Not looked into the root cause yet!

Retr0id2• 3 months ago

Huh why is this getting downvoted?

thom2• 3 months ago

After all these years, we finally have enough eyeballs that all bugs are shallow, and it kinda sucks. How many times a week am I going to be updating my kernel from now on?

brcmthrowaway• 3 months ago

So you think someone is going to break into your house, find your default credentials somehow and get root access?

sureglymop• 3 months ago

With physical access, root access is as simple as setting init=/bin/bash in the kernel parameters from a bootloader. No need for credentials or anything.

thom2• 3 months ago

I think when there’s a step change in our ability to find one type of vulnerability, other types of vulnerability are probably going to become more common as well. Let’s see where we stand at the end of the year.

tempaccount5050• 3 months ago

I haven't updated mine. I have a firewall and it's not exposed to the Internet. Need a key to SSH in. Same with my public facing server. Almost none of these exploits are "drop everything now and patch" unless you are somehow exposing yourself stupidly.

baq3• 3 months ago

If you’re running any sort of CI you’re probably going to have a bad couple of days if everything goes well

rithdmc• 3 months ago

unless you are somehow exposing yourself stupidly

Or, y'know, offer some forms of compute as a service.

INTPenis• 3 months ago

I understand where you're coming from, it's no reason to panic.

But this kind of thinking can be dangerous because it implies that your systems don't talk to the outside world at all, which they obviously do. I mean a very glaring example is container images, so it definitely takes more than a firewall and ssh keys to stay safe in general.

mnw21cam• 3 months ago

It's a "drop everything and patch" if you have a large multi-user server where you don't completely trust all of the users. Like say in a university with a server that students can log in to, like I have just had the joy of updating (and had RHEL break ZFS on me yet again).

But yes, in most other cases no it isn't a "drop everything" exploit - but it does mean one less layer in the multi-layer security, as unprivileged remote exploits now become root-access remote exploits.

bjackman2• 3 months ago

Updating your kernel isn't good enough, it never was.

Native unsandboxed execution == root. Only thing that's new is some people started making websites for their LPEs.

https://github.com/google/security-research/tree/master/pocs...

midtake• 3 months ago

I sort of always expect there to be an LPE to root on Linux tbh, if anything this is great news and Linux might be a useful multiuser system after all.

baq3• 3 months ago

With how things are going the question should be ‘is twice a day often enough?’

dwd• 3 months ago

At the moment it doesn't seem to be.

Within an hour of be advised of, and running the mitigation for DirtyFrag, my upstream provider has blocked all WHM/cPanel/SSH/FTP/SFTP access with a heads-up on:

CVE-2026-29201 CVE-2026-29202 CVE-2026-29203

which look like a repeat of CVE-2026-41940 a week ago.

caned• 3 months ago

The enforcement of read-only protection for pagecache pages (and the scatterlists and or other structures they point to) seems to be diffuse and incredibly fragile.

baggy_trough3• 3 months ago

From the 3rd party discloser:

https://openwall.com/lists/oss-security/2026/05/07/12

SupLockDef• 3 months ago

Where is the famous Linux is so much secure than Windows?

I would like to see the same hate comments about Linux than the ones we would see if it was a Windows vulnerability...

cynicalsecurity• 3 months ago

Imagine how many undiscovered bugs and exploits exist in Windows.

tap-snap-or-nap• 3 months ago

Noone has the time given how many windows bugs are already open and active long term.

netheril962• 3 months ago

We need an easy way to ensure that only kernel modules in an whitelist can load. I’m tired of blacklisting modules I never need.

lyu07282• 3 months ago

Two distro independent LPEs in such a short time, if only all Linux software could be this portable.

mikeweiss• 3 months ago

Considering AWS just released patches for Copy Fail for Amazon Linux and Bottlerocket only yesterday.... I imagine it will over a week before we see patches for this. This is especially important to fix on Kubernetes nodes...does anyone have any recommendations for mitigating this issue before a patch is released?

fulafel4• 3 months ago

Both of these (copy fail and dirtyfrag) exploit obscure socket address families. Are these filtered by commonly used seccomp profiles in eg docker (assuming seccomp can express it)?

YZF• 3 months ago

At least in the k8s setup I looked at the dirtyfrag were filtered (by default).

"XFRM SA registration requires CAP_NET_ADMIN".

fulafel4• 2 months ago

Right, so it blocked the first part of the chain. Which normally uses unprivilgeed network namespace to dp net admin inside that.

I had been thinking of a RxRPC AF block for the second part of the chain which seems rarer.

Systemd seems to have this setting for units since 2011:

The setting RestrictAddressFamilies aims to restrict what socket address families can be used. When using it, the default is that it is used as an allow-list and define what address families can be used.
Example
A common combination might look like this.

   [Service]
   SystemCallArchitectures=native
   RestrictAddressFamilies=AF_INET AF_INET6 AF_UNIX

fulafel4• 3 months ago

RxRPC is apparently an AFS (Andrew File System) thing.

nicman23• 3 months ago

well at least they are not commonly loaded - in like 12 machines i have

RandomGerm4n• 3 months ago

Perhaps we should consider designing distributions to be more tailored to specific purposes. Since no one needs the affected module on a desktop computer, distributions designed for that purpose should no longer include it by default. If this approach were consistently followed, significantly fewer systems would be vulnerable to such exploits. For most users a system with a kernel as minimalistic as the Android GKI kernel combined with sensible SELinux policies, would likely be sufficient.

fulafel4• 3 months ago

Both of the modules are (also) for desktop/workstation use. Though AFS could probably be retired generally.

drmpeg• 3 months ago

Looks like the esp4 and esp6 fixes have been pushed for 7.0, 6.18, 6.12 and 6.6 kernels.

https://lore.kernel.org/lkml/2026050851-iron-hurdle-6421@gre...

https://lore.kernel.org/lkml/2026050843-unplowed-spinster-cf...

https://lore.kernel.org/lkml/2026050832-remold-faceless-bed0...

https://lore.kernel.org/lkml/2026050825-heaving-spender-13a8...

eqvinox13• 3 months ago

And again it's band-aiding the problem. Can authencesn not be fixed or what?

wolttam2• 3 months ago

Maybe write to the LKML if you have some privy information?

titanomachy• 3 months ago

I'm not a security expert, but I'm responsible for some (relatively low-stakes) production systems.

It sounds like these two most recent exploits depend on unprivileged user namespaces, and that in fact a high percentage of LPE exploits need this feature. I use rootless containers on a couple of systems (like my dev machine server), but on most of my systems I don't, so it sounds like disabling that would be a good step to hardening my systems against future exploits.

To the security experts: are there any other straightforward configuration changes with such broad-reaching improvement in security posture? Any well-written guides on this subject, something like "top kernel modules to consider disabling if you don't need them"? I'm not talking about the obvious stuff like "disable password SSH", I'm specifically looking for steps that are statistically likely to prevent as-yet-unknown privilege escalation attacks.

staticassertion9• 3 months ago

You don't need unprivileged user namespaces for this one if you're in a position to get the target kernel module loaded. But yeah, user namespaces are basically the single most significant privesc path in the kernel, maybe io-uring is second. Disabling both (or very carefully deciding what can use them) is one of the best ways to reduce your attack surface.

I don't have any guides but you can determine which kernel modules are already loaded in your system and then just compile those in and block module loading.

Otherwise, shove everything into a container, ideally gvisor, and you've reduced attack surface by a large chunk again via seccomp.

bytejanitor• 3 months ago

Is there a CVE identifier available for this yet?

Luker88• 3 months ago

I can't make it work on nixos. Kernel 7.0.1

I tried fixing the paths and even linking `/bin/bash` to the nix /run/current-system/sw/bin/bash

/etc/passwd is unmodified.

Can anyone else try? CopyFail1 did not work because `su` is only executable, not readable, CopyFail2 worked only partially (changes /etc/passwd but the user is not passwordless)

snvzz• 3 months ago

There's, in practice, unlimited such bugs in the megabytes of kernel object code.

Monolithic UNIX-like kernels are a bankrupt design.

Only third generation microkernels like seL4[0] make sense in the present world. All effort put elsewhere is wasted outright.

0. https://sel4.systems/

danborn26• 3 months ago

The fragmentation logic in the networking stack has been a recurring source of bugs for years. It is surprising how these edge cases keep surviving multiple security audits.

kro2• 3 months ago

It's scary to think that some day it will be more than a local attack vector. I don't want to imagine the fallout from a remote rce via tcp/ip.

nxobject• 3 months ago

I know this was a thing re: Copy Fail, but... ...LPE = "local privilege escalation", for everyone not directly involved in the security.

m3nu• 3 months ago

Ansible playbook to mitigate and verify:

https://gist.github.com/m3nu/d85533bbf342edd3a9426711409a1b9...

Dirty Frag: Universal Linux LPE

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