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Fencer Vulns
medium 4.7

CVE-2026-23394 json

af_unix: Give up GC if MSG_PEEK intervened.

published 2026-03-25 7 mo ago modified 2026-08-19 2 mo ago also EUVD-2026-15396

cvss
4.7
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 0%
public exploits
0
none known

Summary

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.

Patch / fix

  • Linux Linux 6.1.183, 6.6.142, 6.12.92, 6.18.23, 6.19.10, 7.0
  • linux Debian 12 6.1.187-1
  • linux Debian 13 6.12.94-1
  • linux Debian 14 6.19.10-1

debian advisories DEBIAN-CVE-2026-23394

  • linux Ubuntu 24.04 LTS 6.8.0-117.117
  • linux Ubuntu 25.10 6.17.0-29.29
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1055.58
  • linux-aws Ubuntu 25.10 6.17.0-1015.15
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1058.61
  • linux-gcp Ubuntu 25.10 6.17.0-1018.19
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1054.60
  • linux-ibm Ubuntu 24.04 LTS 6.8.0-1055.56

ubuntu advisories UBUNTU-CVE-2026-23394

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.36.1
  • kernel-obs-build Linux Micro Extras 6.2 6.12.0-160000.36.1
  • kernel-rt Linux Micro 6.2 6.12.0-160000.36.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.36.1
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.36.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.36.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.36.1.160000.2.17
  • kernel-azure SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.36.1

suse advisories SUSE-SU-2026:22742-1SUSE-SU-2026:22769-1SUSE-SU-2026:22835-1SUSE-SU-2026:22812-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.36.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.36.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.36.1

opensuse advisories openSUSE-SU-2026:21388-1

  • kernel Azure Linux 3.0 6.6.142.1-1

azure linux advisories AZL-84053

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-23394 updated cvss 5.5

kernel: af_unix: Give up GC if MSG_PEEK intervened

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 10 kernel
    affected: no fix available “Fix deferred”
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.10% chance of exploitation in the next 30 days, higher than 0% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization
Technology feeds

References

Sources

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