Atop 2.11 heap problems

https://openwall.com/lists/oss-security/2025/03/29/1

by baggy_trough • 1 year ago

170 81 1 year ago

Ah, there's the other shoe:)

optional sources, that have to be activated explicitly.

So only locally exploitable, and you have to enable an optional feature? That's ... honestly better than I was worried that it might be

immibis• 1 year ago

always tries to connect

MattPalmer1086• 1 year ago

The fix is to make it optional.

But yeah, I was anticipating something quite a bit worse.

dgacmu• 1 year ago

No. Local but it always tries to connect and the deamon to which it tries to connect is optional, which means that the default is attackable. An attacker can run their own program on the port and send bad strings that will cause an overflow.

yjftsjthsd-h3• 1 year ago

Oh, I see, thanks.

Therefore, the default behavior of atop is now not to connect to the TCP port at all.

I missed that now it defaults to not connecting.

mvdtnz2• 1 year ago

Did you stop reading at that sentence?

yjftsjthsd-h3• 1 year ago

Unlikely, since the use of a local TCP part was later than the quoted sentence. Granted, I did skim, but after having it clarified and rereading, I think that introduction is misleadingly phrased and would benefit from clearer delineation of the previous vulnerable behavior and the fixed behavior.

xyst• 1 year ago

Right, the post on “rachelbythebay” was hinting at something much worse.

brazzy2• 1 year ago

How so? It was pretty clear from her second post that it's a local privilege escalation. And that is is, and otherwise fairly easily exploitable.

echoangle2• 1 year ago

"You might want to stop running atop" - https://news.ycombinator.com/item?id=43477057

"Problems with the heap" - https://news.ycombinator.com/item?id=43485980

dang• 1 year ago

Thanks! Macroexpanded:

Problems with the heap - https://news.ycombinator.com/item?id=43485980 - March 2025 (93 comments)

You might want to stop running atop - https://news.ycombinator.com/item?id=43477057 - March 2025 (139 comments)

unsnap_biceps• 1 year ago

It's unfortunate that Unix sockets isn't being used for local connections like this.

ajross6• 1 year ago

Meh. This isn't a technology choice problem. Routine unix sockets are just some file in /tmp which an attacker could likewise open by racing against the daemon in the same way.

It's true you could use a privileged spot in the filesystem and set things up to use that by writing some simple extra software, but it's equally true that you could lock down a TCP socket to a specific process with about the same amount of work.

Bottom line is that you need to validate your input from outside the process if you're running in a privileged context[1], and atop didn't.

[1] It's not mentioned in the linked email, but I assume the core problem here (and the reason it got a CVE number) is that the atop binary is setuid?

radlad4• 1 year ago

but it's equally true that you could lock down a TCP socket to a specific process with about the same amount of work.

Can you educate me? I'm familiar with SO_PEERCRED that returns the user/group/pid on the other end. Would you then checksum the exe of the pid from /proc?

adrianmonk2• 1 year ago

Routine unix sockets are just some file in /tmp which an attacker could likewise open by racing against the daemon in the same way.

So put the socket in /run instead of /tmp?

I'm no expert, but this appears to be where they belong, and it appears to solve the problem. From https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch03s15.htm... : "System programs that maintain transient UNIX-domain sockets must place them in this directory or an appropriate subdirectory as outlined above." ... "/run should not be writable for unprivileged users; it is a major security problem if any user can write in this directory."

fpoling• 1 year ago

These days Unix sockets for system daemons should be placed under /run with permissions that only a particular daemon can access for binding. With systemd service and socket units it is trivial to do.

3np2• 1 year ago

but it's equally true that you could lock down a TCP socket to a specific process with about the same amount of work.

How, actually? With UNIX sockets it can be a matter of setting file ownership and mode (at worst, a chmod and a chown).

What's the equally simple way to restrict access to a locally listening tcp socket?

eptcyka• 1 year ago

It is. But even with unix sockets, the client should never blindly trust the bytes received and parse them defensively.

lelanthran• 1 year ago

Bottom line is that you need to validate your input from outside the process if you're running in a privileged context[1]

What this "if" qualifier? You need to validate all input from outside the process. Whether the process is privileged or not is, frankly, not really relevant.

(I submitted a blog post a few days ago explaining "Parse, Don't Validate" in plain C, but it didn't get any traction).

charcircuit• 1 year ago

It's more unfortunate a proper RPC library is not being used. People rolling their own buggy parsers in C is an endless source of bugs.

timcobb• 1 year ago

People rolling their own buggy parsers in C

I'd like to believe this isn't common anymore for new projects?

ahoka• 1 year ago

The whole code is horrible: https://github.com/Atoptool/atop/commit/542b7f7ac52926ca2721...

Inconsistent usage of braces, no clear memory ownership or life-cycles, zero tests.

zitterbewegung• 1 year ago

Is it just me or does this seem like a bad design where a TCP port is exposed to share information?

marginalia_nu2• 1 year ago

As long as you bind to localhost it's fine in theory. Though any network code still needs to be rigorously hardened.

echoangle2• 1 year ago

As long as you bind to localhost it's fine in theory

But only if you assume that the data being transferred is public, right?

With the described method, any non-privilieged user could access the data from the TCP socket, right?

kevincox• 1 year ago

Yes. Any local process can connect to a TCP port (unless special care is taken) so it should be a last-resort option. Additionally the sever either needs to be run as root to bind a privileged port or any application can race over binding that port. UNIX sockets are a much better option as they can be protected by filesystem permissions including who can bind the socket and who can connect to it.

This can be mitigated by having authentication inside the socket, but now your authentication code is an attack surface and how are you going to share the secrets? On the filesystem? You are basically back to a UNIX socket with extra steps.

nubinetwork• 1 year ago

atop freaks out if it isn't talking to the thing it thinks it's talking to... who would have thunked it... I feel like a lot of programs have that issue.

kccqzy• 1 year ago

It's acceptable to freak out by crashing. It's even acceptable to crash via explicit assertion failure if the developers don't want to write proper error handling. It's not acceptable to crash via segmentation fault.

dzaima• 1 year ago

It's to an extent even acceptable to crash via segmentation fault (more specifically, doing whatever unsafe exploitable things may come of the source of the issue) if it takes the same amount of privileges to cause the crash as the thing crashing has.

And that's the important thing violated here, atop being rather reasonably ran by root to examine root processes, whereas the exploiter just needs the ability to host a thing on a specific port.

uecker2• 1 year ago

A segmentation fault is perfectly fine as long as an attacker can not cause any other action before it (but I guess this is the case here).

stiild• 1 year ago

I have a semi-related question.For someone whose main job is not maintaining or running full linux servers but would like information about processes and their RAM/CPU..etc. What would be a good tool that is easy to parse with good defaults?

candiddevmike• 1 year ago

Node exporter is a good start, or you could look at Netdata

edoceo• 1 year ago

The tool btop was suggested in the other thread to replace atop and htop.

0manrho• 1 year ago

Seconding btop++, been running it as my main top for a few years now, and switched from htop. I didn't have a single complaint about htop, did what it said on the tin and did it well in my experience, but personally I prefer btop's ux/ui.

calvinmorrison• 1 year ago

htop is a decent curses processes manager that's a few miles better than top

worthless-trash2• 1 year ago

If you are writing software to parse it, dont use third party tooling. Read the kernel outputs directly (/proc/ /sys etc).

While they do have no guarantee not to change, if they do change any tool you are parsing will also be broken.

Zardoz843• 1 year ago

I recommend nmon

ezekiel68• 1 year ago

I recommend.. atop, now that it has been updated to address this issue.

ianbutler3• 1 year ago

Hey guys we commented on another thread from a few days ago about our tool Bismuth finding the bug (along with a sha of our reproducer script for proof) https://news.ycombinator.com/item?id=43489944

After disclosing and having correspondence with Gerlof and from his above post it looks like we did in fact nail it and I've just shared our write up on how we got it.

HN post detailing how we got it: https://news.ycombinator.com/item?id=43519522

Edit: Here's our reproducer and we've added it to the post too: https://gist.github.com/kallsyms/3acdf857ccc5c9fbaae7ed823be...

saagarjha3• 1 year ago

What is that a hash of?

ianbutler3• 1 year ago

As noted, our reproducer script

hannob• 1 year ago

HN post detailing how we got it: https://news.ycombinator.com/item?id=43519522

I don't see any details there. Is there some link missing here, or is it the wrong link?

I'd be interested to read how your tool found it.

stavros• 1 year ago

It's just "we asked our LLM and it found the bug", as I understand it.

taspeotis• 1 year ago

the parsing of the strings is improved to avoid that heap problems can occur.

Tell me what language you’re using without telling me what language you’re using…

geerlingguy• 1 year ago

This doesn't seem nearly as nefarious as the post from earlier this week indicated... I had expected a full supply chain compromise or something that bad based on the earlier post.

f33d5173• 1 year ago

Yeah being taciturn was really the worst thing you could do

barotalomey• 1 year ago

Yea, my first thought was this is a unrelated find because eyeballs since the recent focus.

amiga386• 1 year ago

So, as https://www.cve.org/CVERecord?id=CVE-2025-31160 says:

* CWE-617 Reachable Assertion

* affected from 0 through 2.11.0

... can we assume these will be updated to the actual vulnerability (CWE-940, CWE-120?), and vulnerable versions (2.4.0 through 2.11.0)? Or was the vaguepost about an entirely different vulnerability? Does anyone yet know what specific issue the vaguepost was alluding to?

cullenking• 1 year ago

I was bit by atop a few years back and swore it off. I would get perfectly periodic 10m hangs on MySQL. Apparently they changed the default runtime options such that it used an expensive metric gathering technique with a 10m cron job that would hang any large memory process on the system. It was one of those “no freaking way” revelations after 3 days troubleshooting everything.

Interesting reading through the related submission comments and seeing other hard to troubleshoot bugs. I don’t think atop devs are to blame, my guess is that what you have to do to make a tool like atop work means you are hooking into lots of places that have potential to have unintended consequences.

mvdtnz2• 1 year ago

So what was the point of Rachel's vagueposting? Was there any kind of NDA or a good reason to be so vague?

brazzy2• 1 year ago

Responsible disclosure?

Zardoz843• 1 year ago

omg .. Why a TCP port instead of using a UNIX socket ?

Galanwe• 1 year ago

The vulnerability is caused by the fact that atop always tries to connect to the TCP port of 'atopgpud' during initialization. When another local program has been started (instead of 'atopgpud') that listens to this TCP port, atop connects to that program. Such program is able then to send unexpected strings that may lead to parsing failures in atop. These failures result in heap problems and segmentation faults.

Okay, so, if I have a shell and the rights to listen on a host, I can crash the "atop" of other users? That's it ? I could also create a fork bomb, fill up the disk, use all CPU and memory, etc...

bitbasher• 1 year ago

I think the concern is for privilege escalation.

TonyTrapp• 1 year ago

Not the same thing at all if atop runs as root and you are a user on that system that has no root access. With a well-prepared exploit you could achieve code execution as root. That's a bit more than a simple Denial of Service by filling up the disk.

Havoc• 1 year ago

That sounds less bad than expected

Atop 2.11 heap problems

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