# CVE-2024-35970: af_unix: Clear stale u->oob_skb.

> A race condition in the Linux kernel's AF_UNIX socket handling can cause a deadlock, leading to a denial of service.

- **Severity:** Medium 6.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 May 2024
- **Updated:** 11 May 2026
- **Also known as:** A-432804305, ASB-A-432804305, BELL-CVE-2024-35970, DEBIAN-CVE-2024-35970, GHSA-p8xf-2w27-6wqx, UBUNTU-CVE-2024-35970

## What is CVE-2024-35970?

CVE-2024-35970 is a medium-severity vulnerability in Linux kernel, published on 20 May 2024. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

af_unix: Clear stale u->oob_skb.

syzkaller started to report deadlock of unix_gc_lock after commit
4090fa373f0e ("af_unix: Replace garbage collection algorithm."), but
it just uncovers the bug that has been there since commit 314001f0bf92
("af_unix: Add OOB support").

The repro basically does the following.

  from socket import *
  from array import array

  c1, c2 = socketpair(AF_UNIX, SOCK_STREAM)
  c1.sendmsg([b'a'], [(SOL_SOCKET, SCM_RIGHTS, array("i", [c2.fileno()]))], MSG_OOB)
  c2.recv(1)  # blocked as no normal data in recv queue

  c2.close()  # done async and unblock recv()
  c1.close()  # done async and trigger GC

A socket sends its file descriptor to itself as OOB data and tries to
receive normal data, but finally recv() fails due to async close().

The problem here is wrong handling of OOB skb in manage_oob().  When
recvmsg() is called without MSG_OOB, manage_oob() is called to check
if the peeked skb is OOB skb.  In such a case, manage_oob() pops it
out of the receive queue but does not clear unix_sock(sk)->oob_skb.
This is wrong in terms of uAPI.

Let's say we send "hello" with MSG_OOB, and "world" without MSG_OOB.
The 'o' is handled as OOB data.  When recv() is called twice without
MSG_OOB, the OOB data should be lost.

  >>> from socket import *
  >>> c1, c2 = socketpair(AF_UNIX, SOCK_STREAM, 0)
  >>> c1.send(b'hello', MSG_OOB)  # 'o' is OOB data
  5
  >>> c1.send(b'world')
  5
  >>> c2.recv(5)  # OOB data is not received
  b'hell'
  >>> c2.recv(5)  # OOB date is skipped
  b'world'
  >>> c2.recv(5, MSG_OOB)  # This should return an error
  b'o'

In the same situation, TCP actually returns -EINVAL for the last
recv().

Also, if we do not clear unix_sk(sk)->oob_skb, unix_poll() always set
EPOLLPRI even though the data has passed through by previous recv().

To avoid these issues, we must clear unix_sk(sk)->oob_skb when dequeuing
it from recv queue.

The reason why the old GC did not trigger the deadlock is because the
old GC relied on the receive queue to detect the loop.

When it is triggered, the socket with OOB data is marked as GC candidate
because file refcount == inflight count (1).  However, after traversing
all inflight sockets, the socket still has a positive inflight count (1),
thus the socket is excluded from candidates.  Then, the old GC lose the
chance to garbage-collect the socket.

With the old GC, the repro continues to create true garbage that will
never be freed nor detected by kmemleak as it's linked to the global
inflight list.  That's why we couldn't even notice the issue.

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2024-35970?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-35970?

Apply the vendor's patch.

## Is CVE-2024-35970 being exploited?

There is no known exploitation of CVE-2024-35970 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-35970 and fix it if it is affected.

What it is: CVE-2024-35970 is a medium-severity vulnerability in Linux kernel, published on 20 May 2024. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2024-35970 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2024-35970/ (Markdown: https://insights.sbomify.com/CVE-2024-35970/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-35970
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-35970
- OSV: https://osv.dev/vulnerability/CVE-2024-35970

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-35970/
Summaries are generated and may contain mistakes; the official description above is the record.