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Fencer Vulns
medium 5.5

CVE-2026-52977 json

futex: Prevent lockup in requeue-PI during signal/ timeout wakeup

published 2026-06-24 4 mo ago modified 2026-11-06 2 d ago also EUVD-2026-38845

cvss
5.5
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 2%
public exploits
0
none known

Summary

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

futex: Prevent lockup in requeue-PI during signal/ timeout wakeup

During wait-requeue-pi (task A) and requeue-PI (task B) the following race can happen:

Task A Task B futex_wait_requeue_pi() futex_setup_timer() futex_do_wait() futex_requeue() CLASS(hb, hb1)(&key1); CLASS(hb, hb2)(&key2); *timeout* futex_requeue_pi_wakeup_sync() requeue_state = Q_REQUEUE_PI_IGNORE

*blocks on hb->lock*

futex_proxy_trylock_atomic() futex_requeue_pi_prepare() Q_REQUEUE_PI_IGNORE => -EAGAIN double_unlock_hb(hb1, hb2) *retry*

Task B acquires both hb locks and attempts to acquire the PI-lock of the top most waiter (task B). Task A is leaving early due to a signal/ timeout and started removing itself from the queue. It updates its requeue_state but can not remove it from the list because this requires the hb lock which is owned by task B.

Usually task A is able to swoop the lock after task B unlocked it. However if task B is of higher priority then task A may not be able to wake up in time and acquire the lock before task B gets it again. Especially on a UP system where A is never scheduled.

As a result task A blocks on the lock and task B busy loops, trying to make progress but live locks the system instead. Tragic.

This can be fixed by removing the top most waiter from the list in this case. This allows task B to grab the next top waiter (if any) in the next iteration and make progress.

Remove the top most waiter if futex_requeue_pi_prepare() fails. Let the waiter conditionally remove itself from the list in handle_early_requeue_pi_wakeup().

Patch / fix

  • Linux Linux 5.15.216, 6.1.175, 6.6.141, 6.12.91, 6.18.33, 7.0.10, 7.1
  • linux Debian 12 6.1.176-1
  • linux Debian 13 6.12.94-1
  • linux Debian 14 7.0.10-1

debian advisories DEBIAN-CVE-2026-52977

  • linux Ubuntu 22.04 LTS 5.15.0-198.208
  • linux Ubuntu 24.04 LTS 6.8.0-136.136
  • linux Ubuntu 26.04 LTS 7.0.0-28.28
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1117.124
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1061.64
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1009.9
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1118.128
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1064.72

ubuntu advisories UBUNTU-CVE-2026-52977

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 5.14.0-687.36.1.el9_8
  • rv RHEL 9 5.14.0-687.36.1.el9_8
  • perf RHEL 9 5.14.0-687.36.1.el9_8
  • rtla RHEL 9 5.14.0-687.36.1.el9_8
  • libperf RHEL 9 5.14.0-687.36.1.el9_8
  • kernel-rt RHEL 9 5.14.0-687.36.1.el9_8
  • kernel-64k RHEL 9 5.14.0-687.36.1.el9_8
  • kernel-core RHEL 9 5.14.0-687.36.1.el9_8

red hat advisories RHSA-2026:51035

  • kernel-64kb SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS, SLE High Performance Computing 15 SP5-ESPOS 5.14.21-150500.55.189.1
  • kernel-syms SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.189.1
  • kernel-source SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.189.1
  • kernel-default SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +3 more 5.14.21-150500.55.189.1
  • kernel-obs-build SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.189.1
  • kernel-default-base SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.189.1.150500.6.87.4
  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.81.1
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.81.1

suse advisories SUSE-SU-2026:4595-1SUSE-SU-2026:4254-1SUSE-SU-2026:4369-1SUSE-SU-2026:4347-1SUSE-SU-2026:4284-1SUSE-SU-2026:23887-1

  • 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 5.14.0-687.36.1.el9_8
  • rv AlmaLinux 9 5.14.0-687.36.1.el9_8
  • perf AlmaLinux 9 5.14.0-687.36.1.el9_8
  • rtla AlmaLinux 9 5.14.0-687.36.1.el9_8
  • libperf AlmaLinux 9 5.14.0-687.36.1.el9_8
  • kernel-rt AlmaLinux 9 5.14.0-687.36.1.el9_8
  • kernel-64k AlmaLinux 9 5.14.0-687.36.1.el9_8
  • kernel-core AlmaLinux 9 5.14.0-687.36.1.el9_8

almalinux advisories ALSA-2026:51035

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-2026-52977 updated cvss 5.5

kernel: futex: Prevent lockup in requeue-PI during signal/ timeout wakeup

  • 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 Red Hat Enterprise Linux 10 kernel
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-687.36.1.el9_8, perf 5.14.0-687.36.1.el9_8, rtla 5.14.0-687.36.1.el9_8, python3-perf 5.14.0-687.36.1.el9_8, kernel-devel-matched 5.14.0-687.36.1.el9_8, kernel-64k-devel-matched 5.14.0-687.36.1.el9_8, +7 more Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-687.36.1.el9_8, kernel-64k 5.14.0-687.36.1.el9_8, kernel-core 5.14.0-687.36.1.el9_8, kernel-tools 5.14.0-687.36.1.el9_8, kernel-modules 5.14.0-687.36.1.el9_8, kernel-64k-core 5.14.0-687.36.1.el9_8, +27 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-687.36.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-687.36.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-687.36.1.el9_8, kernel-debuginfo-common-aarch64 5.14.0-687.36.1.el9_8, kernel-debuginfo-common-ppc64le 5.14.0-687.36.1.el9_8 Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-687.36.1.el9_8, kernel-rt-64k 5.14.0-687.36.1.el9_8, kernel-rt-core 5.14.0-687.36.1.el9_8, kernel-rt-modules 5.14.0-687.36.1.el9_8, kernel-rt-64k-core 5.14.0-687.36.1.el9_8, kernel-rt-debug-core 5.14.0-687.36.1.el9_8, +14 more Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-687.36.1.el9_8, kernel-rt-core 5.14.0-687.36.1.el9_8, kernel-rt-modules 5.14.0-687.36.1.el9_8, kernel-rt-debug-core 5.14.0-687.36.1.el9_8, kernel-rt-modules-core 5.14.0-687.36.1.el9_8, kernel-rt-debug-modules 5.14.0-687.36.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:51035
  • 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 SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 d ago

Exploit prediction

0.12% 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
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

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.