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Fencer Vulns
high 7.8

CVE-2026-64560 json

posix-cpu-timers: Prevent UAF caused by non-leader exec() race

published 2026-07-29 3 mo ago modified 2026-11-03 5 d ago also EUVD-2026-50417

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 43%
public exploits
0
none known

Summary

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

posix-cpu-timers: Prevent UAF caused by non-leader exec() race

Wongi and Jungwoo decoded and reported a non-leader exec() related race which can result in an UAF:

sys_timer_delete() exec() posix_cpu_timer_del() // Observes old leader p = pid_task(pid, pid_type); de_thread() switch_leader(); release_task(old_leader) __exit_signal(old_leader) sighand = lock(old_leader, sighand); posix_cpu_timers*_exit(); sighand = lock_task_sighand(p) unhash_task(old_leader); sh = lock(p, sighand) old_leader->sighand = NULL; unlock(sighand); (p->sighand == NULL) unlock(sh) return NULL;

// Returns without action if(!sighand) return 0; free_posix_timer();

This is "harmless" unless the deleted timer was armed and enqueued in p->signal because on exec() a TGID targeted timer is inherited.

As sys_timer_delete() freed the underlying posix timer object run_posix_cpu_timers() or any timerqueue related add/delete operations on other timers will access the freed object's timerqueue node, which results in an UAF.

There is a similar problem vs. posix_cpu_timer_set(). For regular posix timers it just transiently returns -ESRCH to user space, but for the use case in do_cpu_nanosleep() it's the same UAF just that the k_itimer is allocated on the stack.

Also posix_cpu_timer_rearm() fails to rearm the timer, which means it stops to expire.

While debating solutions Frederic pointed out another problem:

posix_cpu_timer_del(tmr) __exit_signal(p) posix_cpu_timers*_exit(p); unhash_task(p); p->sighand = NULL; sh = lock_task_sighand(p) sighand = p->sighand; if (!sighand) return NULL; lock(sighand);

if (!sh) WARN_ON_ONCE(timer_queued(tmr));

On weakly ordered architectures it is not guaranteed that posix_cpu_timer_del() will observe the stores in posix_cpu_timers*_exit() when p->sighand is observed as NULL, which means the WARN() can be a false positive.

Solve these issues by:

1) Changing the store in __exit_signal() to smp_store_release().

2) Adding a smp_acquire__after_ctrl_dep() into the !sighand path of lock_task_sighand().

3) Creating a helper function for looking up the task and locking sighand which does not return when sighand == NULL. Instead it retries the task lookup and only if that fails it gives up.

4) Using that helper in the three affected functions.

#1/#2 ensures that the reader side which observes sighand == NULL also observes all preceeding stores, i.e. the stores in posix_cpu_timers*_exit() and the ones in unhash_task().

#3 ensures that the above described non-leader exec() situation is handled gracefully. When the task lookup returns the old leader, but sighand == NULL then it retries. In the non-leader exec() case the subsequent task lookup will observe the new leader due to #1/#2. In normal exit() scenarios the subsequent lookup fails.

When the task lookup fails, the function also checks whether the timer is still enqueued and issues a warning if that's the case. Unfortunately there is nothing which can be done about it, but as the task is already not longer visible the timer should not be accessed anymore. This check also requires memory ordering, which is not provided when the first lookup fails. To achieve that the check is preceeded by a smp_rmb() which pairs with the smp_wmb() in write_seqlock() in __exit_signal(). That ensures that the stores in posix_cpu_timers*_exit() are visible.

The history of the non-leader exec() issue goes back to the early days of posix CPU timers, which stored a pointer to the group leader task in the timer. That obviously fails when a non-leader exec() switches the leader. commit e0a70217107e ("posix-cpu-timers: workaround to suppress the problems with mt exec") added a temporary workaround for that in 2010 which surv ---truncated---

Patch / fix

  • Linux Linux 5.10.262, 5.15.213, 6.1.180, 6.6.147, 6.12.100, 6.18.41, 7.1.5, 7.2
  • linux Debian 12 6.1.180-1
  • linux Debian 13 6.12.100-1
  • linux Debian 14 7.1.5-1
  • linux-6.12 Debian 12 6.12.100-1~deb12u1

debian advisories DEBIAN-CVE-2026-64560

  • linux Ubuntu 22.04 LTS 5.15.0-198.208
  • linux Ubuntu 24.04 LTS 6.8.0-147.147
  • linux Ubuntu 26.04 LTS 7.0.0-38.38
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1117.124
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1067.70
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1014.14
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1118.128
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1071.79

ubuntu advisories UBUNTU-CVE-2026-64560

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 9 5.14.0-687.41.1.el9_8
  • rv RHEL 9 5.14.0-687.41.1.el9_8
  • perf RHEL 9 5.14.0-687.41.1.el9_8
  • rtla RHEL 9 5.14.0-687.41.1.el9_8
  • libperf RHEL 9 5.14.0-687.41.1.el9_8
  • kernel-rt RHEL 9 5.14.0-687.41.1.el9_8
  • kernel-64k RHEL 9 5.14.0-687.41.1.el9_8
  • kernel-core RHEL 9 5.14.0-687.41.1.el9_8

red hat advisories RHSA-2026:65708RHSA-2026:57252RHSA-2026:57251

  • kernel-default SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Live Patching 15 SP6 +1 more 6.4.0-150600.23.130.1
  • kernel-64kb SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS, SLE High Performance Computing 15 SP5-ESPOS 5.14.21-150500.55.182.1
  • kernel-syms SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.182.1
  • kernel-source SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.182.1
  • kernel-default SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +3 more 5.14.21-150500.55.182.1
  • kernel-obs-build SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.182.1
  • kernel-default-base SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.182.1.150500.6.85.2
  • kernel-rt Real Time Module 15 SP7 6.4.0-150700.7.72.1

suse advisories SUSE-SU-2026:3602-1SUSE-SU-2026:3595-1SUSE-SU-2026:3810-1SUSE-SU-2026:3790-1SUSE-SU-2026:23244-1SUSE-SU-2026:23241-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.37.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.37.1

opensuse advisories openSUSE-SU-2026:21555-1openSUSE-SU-2026:11476-1

  • kernel AlmaLinux 10 6.12.0-211.49.1.el10_2
  • rv AlmaLinux 10 6.12.0-211.49.1.el10_2
  • perf AlmaLinux 10 6.12.0-211.49.1.el10_2
  • rtla AlmaLinux 10 6.12.0-211.49.1.el10_2
  • libperf AlmaLinux 10 6.12.0-211.49.1.el10_2
  • kernel-rt AlmaLinux 10 6.12.0-211.49.1.el10_2
  • kernel-64k AlmaLinux 10 6.12.0-211.49.1.el10_2
  • kernel-core AlmaLinux 10 6.12.0-211.49.1.el10_2

almalinux advisories ALSA-2026:57251ALSA-2026:57252

  • kernel Rocky Linux 10 6.12.0-211.49.1.el10_2
  • kernel Rocky Linux 9 5.14.0-687.41.1.el9_8

rocky linux advisories RLSA-2026:57251RLSA-2026:57252

  • kernel Azure Linux 3.0 6.6.150.1-1

azure linux advisories AZL-94148

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-2026-64560 updated cvss 7.0

kernel: posix-cpu-timers: Prevent UAF caused by non-leader exec() race

  • 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 5.14.0-570.140.1.el9_6, kernel-debuginfo-common-s390x 5.14.0-570.140.1.el9_6, kernel-debuginfo-common-x86_64 5.14.0-570.140.1.el9_6, kernel-debuginfo-common-aarch64 5.14.0-570.140.1.el9_6, kernel-debuginfo-common-ppc64le 5.14.0-570.140.1.el9_6
    fixed: vendor fix RHSA-2026:65708
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-687.41.1.el9_8, perf 5.14.0-687.41.1.el9_8, rtla 5.14.0-687.41.1.el9_8, python3-perf 5.14.0-687.41.1.el9_8, kernel-devel-matched 5.14.0-687.41.1.el9_8, kernel-64k-devel-matched 5.14.0-687.41.1.el9_8, +7 more
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.49.1.el10_2, perf 6.12.0-211.49.1.el10_2, rtla 6.12.0-211.49.1.el10_2, python3-perf 6.12.0-211.49.1.el10_2, kernel-devel-matched 6.12.0-211.49.1.el10_2, kernel-64k-devel-matched 6.12.0-211.49.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:57251
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) rv 5.14.0-570.140.1.el9_6, perf 5.14.0-570.140.1.el9_6, rtla 5.14.0-570.140.1.el9_6, python3-perf 5.14.0-570.140.1.el9_6, kernel-devel-matched 5.14.0-570.140.1.el9_6, kernel-64k-devel-matched 5.14.0-570.140.1.el9_6, +7 more
    fixed: vendor fix RHSA-2026:65708
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-687.41.1.el9_8, kernel-64k 5.14.0-687.41.1.el9_8, kernel-core 5.14.0-687.41.1.el9_8, kernel-tools 5.14.0-687.41.1.el9_8, kernel-modules 5.14.0-687.41.1.el9_8, kernel-64k-core 5.14.0-687.41.1.el9_8, +27 more
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.49.1.el10_2, kernel-64k 6.12.0-211.49.1.el10_2, kernel-core 6.12.0-211.49.1.el10_2, kernel-tools 6.12.0-211.49.1.el10_2, kernel-modules 6.12.0-211.49.1.el10_2, kernel-64k-core 6.12.0-211.49.1.el10_2, +28 more
    fixed: vendor fix RHSA-2026:57251
  • Red Hat Enterprise Linux BaseOS EUS (v.9.6) kernel 5.14.0-570.140.1.el9_6, kernel-64k 5.14.0-570.140.1.el9_6, kernel-core 5.14.0-570.140.1.el9_6, kernel-tools 5.14.0-570.140.1.el9_6, kernel-modules 5.14.0-570.140.1.el9_6, kernel-64k-core 5.14.0-570.140.1.el9_6, +27 more
    fixed: vendor fix RHSA-2026:65708
show 9 more
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-aarch64 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-ppc64le 5.14.0-687.41.1.el9_8
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.49.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.49.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.49.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.49.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.49.1.el10_2
    fixed: vendor fix RHSA-2026:57251
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-687.41.1.el9_8, kernel-rt-64k 5.14.0-687.41.1.el9_8, kernel-rt-core 5.14.0-687.41.1.el9_8, kernel-rt-modules 5.14.0-687.41.1.el9_8, kernel-rt-64k-core 5.14.0-687.41.1.el9_8, kernel-rt-debug-core 5.14.0-687.41.1.el9_8, +14 more
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.49.1.el10_2, kernel-rt-64k 6.12.0-211.49.1.el10_2, kernel-rt-core 6.12.0-211.49.1.el10_2, kernel-rt-modules 6.12.0-211.49.1.el10_2, kernel-rt-64k-core 6.12.0-211.49.1.el10_2, kernel-rt-debug-core 6.12.0-211.49.1.el10_2, +14 more
    fixed: vendor fix RHSA-2026:57251
  • Red Hat Enterprise Linux Real Time EUS (v.9.6) kernel-rt 5.14.0-570.140.1.el9_6, kernel-rt-64k 5.14.0-570.140.1.el9_6, kernel-rt-core 5.14.0-570.140.1.el9_6, kernel-rt-modules 5.14.0-570.140.1.el9_6, kernel-rt-64k-core 5.14.0-570.140.1.el9_6, kernel-rt-debug-core 5.14.0-570.140.1.el9_6, +14 more
    fixed: vendor fix RHSA-2026:65708
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-687.41.1.el9_8, kernel-rt-core 5.14.0-687.41.1.el9_8, kernel-rt-modules 5.14.0-687.41.1.el9_8, kernel-rt-debug-core 5.14.0-687.41.1.el9_8, kernel-rt-modules-core 5.14.0-687.41.1.el9_8, kernel-rt-debug-modules 5.14.0-687.41.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.49.1.el10_2, kernel-rt-core 6.12.0-211.49.1.el10_2, kernel-rt-modules 6.12.0-211.49.1.el10_2, kernel-rt-debug-core 6.12.0-211.49.1.el10_2, kernel-rt-modules-core 6.12.0-211.49.1.el10_2, kernel-rt-debug-modules 6.12.0-211.49.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:57251
  • Red Hat Enterprise Linux Real Time for NFV EUS (v.9.6) kernel-rt 5.14.0-570.140.1.el9_6, kernel-rt-kvm 5.14.0-570.140.1.el9_6, kernel-rt-core 5.14.0-570.140.1.el9_6, kernel-rt-modules 5.14.0-570.140.1.el9_6, kernel-rt-debug-kvm 5.14.0-570.140.1.el9_6, kernel-rt-debug-core 5.14.0-570.140.1.el9_6, +6 more
    fixed: vendor fix RHSA-2026:65708
  • 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, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 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 ICSA-26-295-11 updated cvss 7.8

Siemens SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.7 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.7
    affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

cisa ICSA-26-295-16 updated cvss 7.8

Siemens SIMATIC S7-1500 TM MFP

  • Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
    affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
23 d ago

Exploit prediction

0.50% chance of exploitation in the next 30 days, higher than 43% 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
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
  • Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

Classification

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