CVE-2026-23394
Received Received - Intake
Race Condition in Linux af_unix MSG_PEEK Causes GC Mismanagement

Publication date: 2026-03-25

Last updated on: 2026-04-24

Assigner: kernel.org

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.
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Meta Information
Published
2026-03-25
Last Modified
2026-04-24
Generated
2026-05-07
AI Q&A
2026-03-25
EPSS Evaluated
2026-05-05
NVD
CVE-2026-23394
EUVD
EUVD-2026-15396
Affected Vendors & Products
Showing 12 associated CPEs
Vendor Product Version / Range
linux linux_kernel 6.10
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel From 6.19 (inc) to 6.19.10 (exc)
linux linux_kernel From 6.1.141 (inc) to 6.2 (exc)
linux linux_kernel From 6.10.1 (inc) to 6.18.23 (exc)
linux linux_kernel From 6.6.93 (inc) to 6.7 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-362 The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
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AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability exists in the Linux kernel's af_unix subsystem, where a race condition occurs involving the MSG_PEEK flag and garbage collection (GC) of socket receive queues.

Specifically, when MSG_PEEK is used to peek at data in a socket's receive queue, it silently increments the file reference count without informing the garbage collector. This causes the GC to mistakenly believe that certain sockets are dead and safe to purge, even though they are still alive.

The issue arises in scenarios where one socket (sk-A) is closed but can still be received from via another socket (sk-B). If sk-B uses MSG_PEEK on sk-A's data and then sk-B is closed while GC is checking the sockets, the GC may incorrectly conclude both sockets are dead and purge them.

The root cause is that MSG_PEEK increments the file reference count without synchronizing with the GC, leading to an invalid evaluation of socket liveness. The fix involves signaling the race condition using a memory barrier and deferring garbage collection to avoid incorrect purging.


How can this vulnerability impact me? :

This vulnerability can lead to premature garbage collection of active sockets in the Linux kernel, which may cause unexpected socket closures or data loss.

Applications relying on Unix domain sockets for inter-process communication might experience disruptions, as the kernel could mistakenly purge sockets that are still in use.

Such unexpected socket purging could result in application errors, communication failures, or potential denial of service conditions if critical socket connections are closed unexpectedly.


What immediate steps should I take to mitigate this vulnerability?

The vulnerability has been resolved in the Linux kernel by modifying the garbage collection (GC) mechanism related to AF_UNIX sockets and MSG_PEEK usage.

To mitigate this vulnerability immediately, you should update your Linux kernel to a version that includes the fix described, which involves using seqcount_t to notify GC when MSG_PEEK occurs and deferring SCC garbage collection to avoid race conditions.

No specific workaround commands or configuration changes are provided in the available information, so applying the kernel update is the recommended immediate step.


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