# CVE-2026-23394: af_unix: Give up GC if MSG_PEEK intervened.

> A race condition in Linux kernel Unix socket garbage collection allows an attacker to cause denial of service by purging receive queues of alive sockets.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Mar 2026
- **Updated:** 19 Aug 2026
- **Also known as:** AZL-84053, BELL-CVE-2026-23394, DEBIAN-CVE-2026-23394, GHSA-p5pc-67g7-qcv2, ROOT-OS-DEBIAN-12-CVE-2026-23394, ROOT-OS-DEBIAN-13-CVE-2026-23394, ROOT-OS-UBUNTU-2404-CVE-2026-23394, UBUNTU-CVE-2026-23394

## What is CVE-2026-23394?

CVE-2026-23394 is a medium-severity vulnerability in Linux kernel, published on 25 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

af_unix: Give up GC if MSG_PEEK intervened.

Igor Ushakov reported that GC purged the receive queue of
an alive socket due to a race with MSG_PEEK with a nice repro.

This is the exact same issue previously fixed by commit
cbcf01128d0a ("af_unix: fix garbage collect vs MSG_PEEK").

After GC was replaced with the current algorithm, the cited
commit removed the locking dance in unix_peek_fds() and
reintroduced the same issue.

The problem is that MSG_PEEK bumps a file refcount without
interacting with GC.

Consider an SCC containing sk-A and sk-B, where sk-A is
close()d but can be recv()ed via sk-B.

The bad thing happens if sk-A is recv()ed with MSG_PEEK from
sk-B and sk-B is close()d while GC is checking unix_vertex_dead()
for sk-A and sk-B.

  GC thread                    User thread
  ---------                    -----------
  unix_vertex_dead(sk-A)
  -> true   <------.
                    \
                     `------   recv(sk-B, MSG_PEEK)
              invalidate !!    -> sk-A's file refcount : 1 -> 2

                               close(sk-B)
                               -> sk-B's file refcount : 2 -> 1
  unix_vertex_dead(sk-B)
  -> true

Initially, sk-A's file refcount is 1 by the inflight fd in sk-B
recvq.  GC thinks sk-A is dead because the file refcount is the
same as the number of its inflight fds.

However, sk-A's file refcount is bumped silently by MSG_PEEK,
which invalidates the previous evaluation.

At this moment, sk-B's file refcount is 2; one by the open fd,
and one by the inflight fd in sk-A.  The subsequent close()
releases one refcount by the former.

Finally, GC incorrectly concludes that both sk-A and sk-B are dead.

One option is to restore the locking dance in unix_peek_fds(),
but we can resolve this more elegantly thanks to the new algorithm.

The point is that the issue does not occur without the subsequent
close() and we actually do not need to synchronise MSG_PEEK with
the dead SCC detection.

When the issue occurs, close() and GC touch the same file refcount.
If GC sees the refcount being decremented by close(), it can just
give up garbage-collecting the SCC.

Therefore, we only need to signal the race during MSG_PEEK with
a proper memory barrier to make it visible to the GC.

Let's use seqcount_t to notify GC when MSG_PEEK occurs and let
it defer the SCC to the next run.

This way no locking is needed on the MSG_PEEK side, and we can
avoid imposing a penalty on every MSG_PEEK unnecessarily.

Note that we can retry within unix_scc_dead() if MSG_PEEK is
detected, but we do not do so to avoid hung task splat from
abusive MSG_PEEK calls.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-23394?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23394?

Apply the vendor's patch.

## Is CVE-2026-23394 being exploited?

There is no known exploitation of CVE-2026-23394 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-2026-23394 and fix it if it is affected.

What it is: CVE-2026-23394 is a medium-severity vulnerability in Linux kernel, published on 25 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-23394 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-2026-23394/ (Markdown: https://insights.sbomify.com/CVE-2026-23394/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23394
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23394
- OSV: https://osv.dev/vulnerability/CVE-2026-23394

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23394/
Summaries are generated and may contain mistakes; the official description above is the record.