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Fencer Vulns
high 7.8

CVE-2025-38349 json

eventpoll: don't decrement ep refcount while still holding the ep mutex

published 2025-07-18 15 mo ago modified 2026-10-03 37 d ago also EUVD-2025-21860

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 8%
public exploits
0
none known

Summary

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

eventpoll: don't decrement ep refcount while still holding the ep mutex

Jann Horn points out that epoll is decrementing the ep refcount and then doing a

mutex_unlock(&ep->mtx);

afterwards. That's very wrong, because it can lead to a use-after-free.

That pattern is actually fine for the very last reference, because the code in question will delay the actual call to "ep_free(ep)" until after it has unlocked the mutex.

But it's wrong for the much subtler "next to last" case when somebody *else* may also be dropping their reference and free the ep while we're still using the mutex.

Note that this is true even if that other user is also using the same ep mutex: mutexes, unlike spinlocks, can not be used for object ownership, even if they guarantee mutual exclusion.

A mutex "unlock" operation is not atomic, and as one user is still accessing the mutex as part of unlocking it, another user can come in and get the now released mutex and free the data structure while the first user is still cleaning up.

See our mutex documentation in Documentation/locking/mutex-design.rst, in particular the section [1] about semantics:

"mutex_unlock() may access the mutex structure even after it has internally released the lock already - so it's not safe for another context to acquire the mutex and assume that the mutex_unlock() context is not using the structure anymore"

So if we drop our ep ref before the mutex unlock, but we weren't the last one, we may then unlock the mutex, another user comes in, drops _their_ reference and releases the 'ep' as it now has no users - all while the mutex_unlock() is still accessing it.

Fix this by simply moving the ep refcount dropping to outside the mutex: the refcount itself is atomic, and doesn't need mutex protection (that's the whole _point_ of refcounts: unlike mutexes, they are inherently about object lifetimes).

Patch / fix

  • Linux Linux 5.15.222, 6.1.178, 6.6.99, 6.12.39, 6.15.7, 6.16
  • linux Debian 13 6.12.41-1
  • linux Debian 14 6.16.3-1

debian advisories DEBIAN-CVE-2025-38349

  • linux Ubuntu 22.04 LTS 5.15.0-202.212
  • linux Ubuntu 24.04 LTS 6.8.0-100.100
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1119.126
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1046.49
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1120.130
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1047.50
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1115.121
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1043.48

ubuntu advisories UBUNTU-CVE-2025-38349

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 RHEL 10.1 6.12.0-124.31.1.el10_1
  • rv RHEL 10.1 6.12.0-124.31.1.el10_1
  • perf RHEL 10.1 6.12.0-124.31.1.el10_1
  • rtla RHEL 10.1 6.12.0-124.31.1.el10_1
  • libperf RHEL 10.1 6.12.0-124.31.1.el10_1
  • kernel-rt RHEL 10.1 6.12.0-124.31.1.el10_1
  • kernel-64k RHEL 10.1 6.12.0-124.31.1.el10_1
  • kernel-core RHEL 10.1 6.12.0-124.31.1.el10_1

red hat advisories RHSA-2026:4111RHSA-2026:2759RHSA-2026:1690RHSA-2026:1143

  • kernel-rt Linux Micro 6.2 6.12.0-160000.6.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.6.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1.160000.2.4
  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1
  • kernel-obs-qa SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.6.1
  • kernel-kvmsmall SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.6.1

suse advisories SUSE-SU-2025:21074-1SUSE-SU-2025:21139-1SUSE-SU-2026:20560-1SUSE-SU-2025:21179-1SUSE-SU-2025:03023-1SUSE-SU-2025:03011-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.6.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-kvmsmall openSUSE Leap 16.0 6.12.0-160000.6.1

opensuse advisories openSUSE-SU-2025:20081-1

  • kernel-abi-stablelists AlmaLinux 10 6.12.0-124.31.1.el10_1
  • kernel AlmaLinux 9 5.14.0-611.26.1.el9_7
  • rv AlmaLinux 9 5.14.0-611.26.1.el9_7
  • perf AlmaLinux 9 5.14.0-611.26.1.el9_7
  • rtla AlmaLinux 9 5.14.0-611.26.1.el9_7
  • libperf AlmaLinux 9 5.14.0-611.26.1.el9_7
  • kernel-rt AlmaLinux 9 5.14.0-611.26.1.el9_7
  • kernel-64k AlmaLinux 9 5.14.0-611.26.1.el9_7

almalinux advisories ALSA-2026:1690ALSA-2026:1143

  • kernel Rocky Linux 10 6.12.0-124.31.1.el10_1
  • kernel Rocky Linux 9 5.14.0-611.26.1.el9_7

rocky linux advisories RLSA-2026:1690RLSA-2026:1143

  • kernel Azure Linux 3.0 6.6.104.2-1

azure linux advisories AZL-65544

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-2025-38349 updated cvss 7.0

kernel: Linux kernel use-after-free in eventpoll

  • Red Hat Enterprise Linux 7 kernel-rt, kernel-rt-kvm, kernel-rt-trace, kernel-rt-debug-kvm, kernel-rt-trace-kvm Red Hat Enterprise Linux 8 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +6 more Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more
    affected: no fix available
  • Red Hat CodeReady Linux Builder EUS (v.9.6) libperf 5.14.0-570.89.1.el9_6, kernel-debuginfo-common-s390x 5.14.0-570.89.1.el9_6, kernel-debuginfo-common-x86_64 5.14.0-570.89.1.el9_6, kernel-debuginfo-common-aarch64 5.14.0-570.89.1.el9_6, kernel-debuginfo-common-ppc64le 5.14.0-570.89.1.el9_6
    fixed: vendor fix RHSA-2026:2759
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-611.26.1.el9_7, perf 5.14.0-611.26.1.el9_7, rtla 5.14.0-611.26.1.el9_7, python3-perf 5.14.0-611.26.1.el9_7, kernel-devel-matched 5.14.0-611.26.1.el9_7, kernel-64k-devel-matched 5.14.0-611.26.1.el9_7, +7 more
    fixed: vendor fix RHSA-2026:1143
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-124.31.1.el10_1, perf 6.12.0-124.31.1.el10_1, rtla 6.12.0-124.31.1.el10_1, python3-perf 6.12.0-124.31.1.el10_1, kernel-devel-matched 6.12.0-124.31.1.el10_1, kernel-64k-devel-matched 6.12.0-124.31.1.el10_1, +7 more
    fixed: vendor fix RHSA-2026:1690
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) rv 6.12.0-55.63.1.el10_0, perf 6.12.0-55.63.1.el10_0, rtla 6.12.0-55.63.1.el10_0, python3-perf 6.12.0-55.63.1.el10_0, kernel-devel-matched 6.12.0-55.63.1.el10_0, kernel-64k-devel-matched 6.12.0-55.63.1.el10_0, +7 more
    fixed: vendor fix RHSA-2026:4111
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) rv 5.14.0-570.89.1.el9_6, perf 5.14.0-570.89.1.el9_6, rtla 5.14.0-570.89.1.el9_6, python3-perf 5.14.0-570.89.1.el9_6, kernel-devel-matched 5.14.0-570.89.1.el9_6, kernel-64k-devel-matched 5.14.0-570.89.1.el9_6, +7 more
    fixed: vendor fix RHSA-2026:2759
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-611.26.1.el9_7, kernel-64k 5.14.0-611.26.1.el9_7, kernel-core 5.14.0-611.26.1.el9_7, kernel-tools 5.14.0-611.26.1.el9_7, kernel-modules 5.14.0-611.26.1.el9_7, kernel-64k-core 5.14.0-611.26.1.el9_7, +27 more
    fixed: vendor fix RHSA-2026:1143
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-124.31.1.el10_1, kernel-64k 6.12.0-124.31.1.el10_1, kernel-core 6.12.0-124.31.1.el10_1, kernel-tools 6.12.0-124.31.1.el10_1, kernel-modules 6.12.0-124.31.1.el10_1, kernel-64k-core 6.12.0-124.31.1.el10_1, +28 more
    fixed: vendor fix RHSA-2026:1690
show 14 more
  • Red Hat Enterprise Linux BaseOS EUS (v. 10.0) kernel 6.12.0-55.63.1.el10_0, kernel-64k 6.12.0-55.63.1.el10_0, kernel-core 6.12.0-55.63.1.el10_0, kernel-tools 6.12.0-55.63.1.el10_0, kernel-modules 6.12.0-55.63.1.el10_0, kernel-64k-core 6.12.0-55.63.1.el10_0, +27 more
    fixed: vendor fix RHSA-2026:4111
  • Red Hat Enterprise Linux BaseOS EUS (v.9.6) kernel 5.14.0-570.89.1.el9_6, kernel-64k 5.14.0-570.89.1.el9_6, kernel-core 5.14.0-570.89.1.el9_6, kernel-tools 5.14.0-570.89.1.el9_6, kernel-modules 5.14.0-570.89.1.el9_6, kernel-64k-core 5.14.0-570.89.1.el9_6, +27 more
    fixed: vendor fix RHSA-2026:2759
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-611.26.1.el9_7, kernel-debuginfo-common-s390x 5.14.0-611.26.1.el9_7, kernel-debuginfo-common-x86_64 5.14.0-611.26.1.el9_7, kernel-debuginfo-common-aarch64 5.14.0-611.26.1.el9_7, kernel-debuginfo-common-ppc64le 5.14.0-611.26.1.el9_7
    fixed: vendor fix RHSA-2026:1143
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-124.31.1.el10_1, kernel-debuginfo-common-s390x 6.12.0-124.31.1.el10_1, kernel-debuginfo-common-x86_64 6.12.0-124.31.1.el10_1, kernel-debuginfo-common-aarch64 6.12.0-124.31.1.el10_1, kernel-debuginfo-common-ppc64le 6.12.0-124.31.1.el10_1
    fixed: vendor fix RHSA-2026:1690
  • Red Hat Enterprise Linux CodeReady Linux Builder EUS (v. 10.0) libperf 6.12.0-55.63.1.el10_0, kernel-debuginfo-common-s390x 6.12.0-55.63.1.el10_0, kernel-debuginfo-common-x86_64 6.12.0-55.63.1.el10_0, kernel-debuginfo-common-aarch64 6.12.0-55.63.1.el10_0, kernel-debuginfo-common-ppc64le 6.12.0-55.63.1.el10_0
    fixed: vendor fix RHSA-2026:4111
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-611.26.1.el9_7, kernel-rt-64k 5.14.0-611.26.1.el9_7, kernel-rt-core 5.14.0-611.26.1.el9_7, kernel-rt-modules 5.14.0-611.26.1.el9_7, kernel-rt-64k-core 5.14.0-611.26.1.el9_7, kernel-rt-debug-core 5.14.0-611.26.1.el9_7, +14 more
    fixed: vendor fix RHSA-2026:1143
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-124.31.1.el10_1, kernel-rt-64k 6.12.0-124.31.1.el10_1, kernel-rt-core 6.12.0-124.31.1.el10_1, kernel-rt-modules 6.12.0-124.31.1.el10_1, kernel-rt-64k-core 6.12.0-124.31.1.el10_1, kernel-rt-debug-core 6.12.0-124.31.1.el10_1, +14 more
    fixed: vendor fix RHSA-2026:1690
  • Red Hat Enterprise Linux Real Time EUS (v. 10.0) kernel-rt 6.12.0-55.63.1.el10_0, kernel-rt-64k 6.12.0-55.63.1.el10_0, kernel-rt-core 6.12.0-55.63.1.el10_0, kernel-rt-modules 6.12.0-55.63.1.el10_0, kernel-rt-64k-core 6.12.0-55.63.1.el10_0, kernel-rt-debug-core 6.12.0-55.63.1.el10_0, +14 more
    fixed: vendor fix RHSA-2026:4111
  • Red Hat Enterprise Linux Real Time EUS (v.9.6) kernel-rt 5.14.0-570.89.1.el9_6, kernel-rt-64k 5.14.0-570.89.1.el9_6, kernel-rt-core 5.14.0-570.89.1.el9_6, kernel-rt-modules 5.14.0-570.89.1.el9_6, kernel-rt-64k-core 5.14.0-570.89.1.el9_6, kernel-rt-debug-core 5.14.0-570.89.1.el9_6, +14 more
    fixed: vendor fix RHSA-2026:2759
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-611.26.1.el9_7, kernel-rt-core 5.14.0-611.26.1.el9_7, kernel-rt-modules 5.14.0-611.26.1.el9_7, kernel-rt-debug-core 5.14.0-611.26.1.el9_7, kernel-rt-modules-core 5.14.0-611.26.1.el9_7, kernel-rt-debug-modules 5.14.0-611.26.1.el9_7, +4 more
    fixed: vendor fix RHSA-2026:1143
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-124.31.1.el10_1, kernel-rt-core 6.12.0-124.31.1.el10_1, kernel-rt-modules 6.12.0-124.31.1.el10_1, kernel-rt-debug-core 6.12.0-124.31.1.el10_1, kernel-rt-modules-core 6.12.0-124.31.1.el10_1, kernel-rt-debug-modules 6.12.0-124.31.1.el10_1, +4 more
    fixed: vendor fix RHSA-2026:1690
  • Red Hat Enterprise Linux Real Time for NFV EUS (v. 10.0) kernel-rt 6.12.0-55.63.1.el10_0, kernel-rt-kvm 6.12.0-55.63.1.el10_0, kernel-rt-core 6.12.0-55.63.1.el10_0, kernel-rt-modules 6.12.0-55.63.1.el10_0, kernel-rt-debug-kvm 6.12.0-55.63.1.el10_0, kernel-rt-debug-core 6.12.0-55.63.1.el10_0, +6 more
    fixed: vendor fix RHSA-2026:4111
  • Red Hat Enterprise Linux Real Time for NFV EUS (v.9.6) kernel-rt 5.14.0-570.89.1.el9_6, kernel-rt-kvm 5.14.0-570.89.1.el9_6, kernel-rt-core 5.14.0-570.89.1.el9_6, kernel-rt-modules 5.14.0-570.89.1.el9_6, kernel-rt-debug-kvm 5.14.0-570.89.1.el9_6, kernel-rt-debug-core 5.14.0-570.89.1.el9_6, +6 more
    fixed: vendor fix RHSA-2026:2759
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, python-perf, kernel-kdump, kernel-tools, +3 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-core, kernel-tools, python3-perf, +17 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

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
4 mo ago

Exploit prediction

0.18% chance of exploitation in the next 30 days, higher than 8% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.