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Fencer Vulns
high 7.8

CVE-2026-53341 json

fhandle: fix UAF due to unlocked ->mnt_ns read in may_decode_fh()

published 2026-07-01 4 mo ago modified 2026-10-19 20 d ago also EUVD-2026-40975

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 2%
public exploits
0
none known

Summary

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

fhandle: fix UAF due to unlocked ->mnt_ns read in may_decode_fh()

may_decode_fh() accesses mount::mnt_ns without holding any locks; that means the mount can concurrently be unmounted, and the mnt_namespace can concurrently be freed after an RCU grace period.

This race can happens as follows, assuming that the mount point was created by open_tree(..., OPEN_TREE_CLONE):

thread 1 thread 2 RCU __do_sys_open_by_handle_at do_handle_open handle_to_path may_decode_fh is_mounted [mount::mnt_ns access] [mount::mnt_ns access] __do_sys_close fput_close_sync __fput dissolve_on_fput umount_tree class_namespace_excl_destructor namespace_unlock free_mnt_ns mnt_ns_tree_remove call_rcu(mnt_ns_release_rcu) mnt_ns_release_rcu mnt_ns_release kfree [mnt_namespace::user_ns access] **UAF**

Fix it by taking rcu_read_lock() around the mount::mnt_ns access, like in __prepend_path(). Additionally, document the semantics of mount::mnt_ns, and use WRITE_ONCE() for writers that can race with lockless readers.

This bug is unreachable unless one of the following is set:

- CONFIG_PREEMPTION - CONFIG_RCU_STRICT_GRACE_PERIOD

because it requires an RCU grace period to happen during a syscall without an explicit preemption.

This doesn't seem to have interesting security impact; worst-case, it could leak the result of an integer comparison to userspace (from the level check in cap_capable()), cause an endless loop, or crash the kernel by dereferencing an invalid address.

Patch / fix

  • Linux Linux 6.12.95, 6.18.36, 7.0.13, 7.1
  • linux Debian 13 6.12.95-1
  • linux Debian 14 7.0.13-1

debian advisories DEBIAN-CVE-2026-53341

  • linux Ubuntu 26.04 LTS 7.0.0-31.31
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1012.12
  • linux-gcp Ubuntu 26.04 LTS 7.0.0-1011.11
  • linux-gke Ubuntu 26.04 LTS 7.0.0-1006.7
  • linux-ibm Ubuntu 26.04 LTS 7.0.0-1013.13
  • linux-azure Ubuntu 26.04 LTS 7.0.0-1014.14
  • linux-raspi Ubuntu 26.04 LTS 7.0.0-1019.19
  • linux-riscv Ubuntu 26.04 LTS 7.0.0-31.31.1

ubuntu advisories UBUNTU-CVE-2026-53341

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 10.2 6.12.0-211.61.1.el10_2
  • rv RHEL 10.2 6.12.0-211.61.1.el10_2
  • perf RHEL 10.2 6.12.0-211.61.1.el10_2
  • rtla RHEL 10.2 6.12.0-211.61.1.el10_2
  • libperf RHEL 10.2 6.12.0-211.61.1.el10_2
  • kernel-rt RHEL 10.2 6.12.0-211.61.1.el10_2
  • kernel-64k RHEL 10.2 6.12.0-211.61.1.el10_2
  • kernel-core RHEL 10.2 6.12.0-211.61.1.el10_2

red hat advisories RHSA-2026:72624RHSA-2026:72623

  • kernel-rt Linux Micro 6.2 6.12.0-160000.38.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.38.1
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.38.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.38.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.38.1.160000.2.23
  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.38.1
  • kernel-azure SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.38.1
  • kernel-obs-qa SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.38.1

suse advisories SUSE-SU-2026:23887-1SUSE-SU-2026:23902-1SUSE-SU-2026:23897-1SUSE-SU-2026:23881-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.38.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.38.1

opensuse advisories openSUSE-SU-2026:21910-1

  • kernel AlmaLinux 9 5.14.0-687.53.1.el9_8
  • rv AlmaLinux 9 5.14.0-687.53.1.el9_8
  • perf AlmaLinux 9 5.14.0-687.53.1.el9_8
  • rtla AlmaLinux 9 5.14.0-687.53.1.el9_8
  • libperf AlmaLinux 9 5.14.0-687.53.1.el9_8
  • kernel-rt AlmaLinux 9 5.14.0-687.53.1.el9_8
  • kernel-64k AlmaLinux 9 5.14.0-687.53.1.el9_8
  • kernel-core AlmaLinux 9 5.14.0-687.53.1.el9_8

almalinux advisories ALSA-2026:72623ALSA-2026:72624

  • kernel Rocky Linux 10 6.12.0-211.61.1.el10_2
  • kernel Rocky Linux 9 5.14.0-687.53.1.el9_8

rocky linux advisories RLSA-2026:72624RLSA-2026:72623

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-2026-53341 updated cvss 4.7

kernel: fhandle: fix UAF due to unlocked ->mnt_ns read in may_decode_fh()

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-687.53.1.el9_8, perf 5.14.0-687.53.1.el9_8, rtla 5.14.0-687.53.1.el9_8, python3-perf 5.14.0-687.53.1.el9_8, kernel-devel-matched 5.14.0-687.53.1.el9_8, kernel-64k-devel-matched 5.14.0-687.53.1.el9_8, +7 more
    fixed: vendor fix RHSA-2026:72623
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.61.1.el10_2, perf 6.12.0-211.61.1.el10_2, rtla 6.12.0-211.61.1.el10_2, python3-perf 6.12.0-211.61.1.el10_2, kernel-devel-matched 6.12.0-211.61.1.el10_2, kernel-64k-devel-matched 6.12.0-211.61.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:72624
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-687.53.1.el9_8, kernel-64k 5.14.0-687.53.1.el9_8, kernel-core 5.14.0-687.53.1.el9_8, kernel-tools 5.14.0-687.53.1.el9_8, kernel-modules 5.14.0-687.53.1.el9_8, kernel-64k-core 5.14.0-687.53.1.el9_8, +27 more
    fixed: vendor fix RHSA-2026:72623
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.61.1.el10_2, kernel-64k 6.12.0-211.61.1.el10_2, kernel-core 6.12.0-211.61.1.el10_2, kernel-tools 6.12.0-211.61.1.el10_2, kernel-modules 6.12.0-211.61.1.el10_2, kernel-64k-core 6.12.0-211.61.1.el10_2, +28 more
    fixed: vendor fix RHSA-2026:72624
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-687.53.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-687.53.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-687.53.1.el9_8, kernel-debuginfo-common-aarch64 5.14.0-687.53.1.el9_8, kernel-debuginfo-common-ppc64le 5.14.0-687.53.1.el9_8
    fixed: vendor fix RHSA-2026:72623
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.61.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.61.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.61.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.61.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.61.1.el10_2
    fixed: vendor fix RHSA-2026:72624
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-687.53.1.el9_8, kernel-rt-64k 5.14.0-687.53.1.el9_8, kernel-rt-core 5.14.0-687.53.1.el9_8, kernel-rt-modules 5.14.0-687.53.1.el9_8, kernel-rt-64k-core 5.14.0-687.53.1.el9_8, kernel-rt-debug-core 5.14.0-687.53.1.el9_8, +14 more
    fixed: vendor fix RHSA-2026:72623
show 4 more
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.61.1.el10_2, kernel-rt-64k 6.12.0-211.61.1.el10_2, kernel-rt-core 6.12.0-211.61.1.el10_2, kernel-rt-modules 6.12.0-211.61.1.el10_2, kernel-rt-64k-core 6.12.0-211.61.1.el10_2, kernel-rt-debug-core 6.12.0-211.61.1.el10_2, +14 more
    fixed: vendor fix RHSA-2026:72624
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-687.53.1.el9_8, kernel-rt-core 5.14.0-687.53.1.el9_8, kernel-rt-modules 5.14.0-687.53.1.el9_8, kernel-rt-debug-core 5.14.0-687.53.1.el9_8, kernel-rt-modules-core 5.14.0-687.53.1.el9_8, kernel-rt-debug-modules 5.14.0-687.53.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:72623
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.61.1.el10_2, kernel-rt-core 6.12.0-211.61.1.el10_2, kernel-rt-modules 6.12.0-211.61.1.el10_2, kernel-rt-debug-core 6.12.0-211.61.1.el10_2, kernel-rt-modules-core 6.12.0-211.61.1.el10_2, kernel-rt-debug-modules 6.12.0-211.61.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:72624
  • 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 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 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
23 d ago

Exploit prediction

0.13% chance of exploitation in the next 30 days, higher than 2% 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

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.