Summaryinfo

A vulnerability categorized as critical has been discovered in Linux Kernel up to 6.19.9/7.0-rc4. This issue affects the function unix_peek_fds of the component af_unix. Such manipulation leads to reference count. This vulnerability is referenced as CVE-2026-23394. No exploit is available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.19.9/7.0-rc4. It has been rated as critical. Affected by this issue is the function unix_peek_fds of the component af_unix. The manipulation with an unknown input leads to a reference count vulnerability. Using CWE to declare the problem leads to CWE-911. The product uses a reference count to manage a resource, but it does not update or incorrectly updates the reference count. Impacted is availability. CVE summarizes:

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.

The advisory is shared for download at git.kernel.org. This vulnerability is handled as CVE-2026-23394 since 01/13/2026. The exploitation is known to be difficult. There are known technical details, but no exploit is available.

Upgrading to version 6.19.10 or 7.0-rc5 eliminates this vulnerability. Applying the patch 37dd7ab332396eb8dd80b2dc7ea4b61abf767436/e5b31d988a41549037b8d8721a3c3cae893d8670 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.19.0
• 6.19.1
• 6.19.2
• 6.19.3
• 6.19.4
• 6.19.5
• 6.19.6
• 6.19.7
• 6.19.8
• 6.19.9
• 7.0-rc1
• 7.0-rc2
• 7.0-rc3
• 7.0-rc4

License

• open-source

Website

• Vendor: https://www.kernel.org/

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