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Unscored CVE-2025-68214 EUVD-2025-203682GHSA-q35m-cwfx-j6jx

timers: Fix NULL function pointer race in timer_shutdown_sync()

Published Dec 16, 2025 · Updated Nov 5, 2026 · Assigned by Linux

Vendor: Linux Product: Linux Package: kernel Package: linux Package: linux Package: linux-allwinner-5.19 Package: linux-aws Package: linux-aws-5.0 Package: linux-aws-5.11 Package: linux-aws-5.13 Package: linux-aws-5.15 Package: linux-aws-5.19 Package: linux-aws-5.3 Package: linux-aws-5.4 Package: linux-aws-5.8 Package: linux-aws-6.14 Package: linux-aws-6.17 Package: linux-aws-6.2 Package: linux-aws-6.5 Package: linux-aws-6.8 Package: linux-aws-fips Package: linux-azure Package: linux-azure-5.11 Package: linux-azure-5.13 Package: linux-azure-5.15 Package: linux-azure-5.19 Package: linux-azure-5.3 Package: linux-azure-5.4 Package: linux-azure-5.8 Package: linux-azure-6.11 Package: linux-azure-6.14 Package: linux-azure-6.17 Package: linux-azure-6.2 Package: linux-azure-6.5 Package: linux-azure-6.8 Package: linux-azure-edge Package: linux-azure-fde Package: linux-azure-fde-5.15 Package: linux-azure-fde-5.19 Package: linux-azure-fde-6.14 Package: linux-azure-fde-6.2 Package: linux-azure-fde-6.8 Package: linux-azure-fips Package: linux-azure-nvidia Package: linux-azure-nvidia-6.14 Package: linux-bluefield Package: linux-fips Package: linux-gcp Package: linux-gcp-5.11 Package: linux-gcp-5.13 Package: linux-gcp-5.15 Package: linux-gcp-5.19 Package: linux-gcp-5.3 Package: linux-gcp-5.4 Package: linux-gcp-5.8 Package: linux-gcp-6.11 Package: linux-gcp-6.14 Package: linux-gcp-6.17 Package: linux-gcp-6.2 Package: linux-gcp-6.5 Package: linux-gcp-6.8 Package: linux-gcp-fips Package: linux-gke Package: linux-gke-4.15 Package: linux-gke-5.15 Package: linux-gke-5.4 Package: linux-gkeop Package: linux-gkeop-5.15 Package: linux-gkeop-5.4 Package: linux-hwe Package: linux-hwe-5.11 Package: linux-hwe-5.13 Package: linux-hwe-5.15 Package: linux-hwe-5.19 Package: linux-hwe-5.4 Package: linux-hwe-5.8 Package: linux-hwe-6.11 Package: linux-hwe-6.14 Package: linux-hwe-6.17 Package: linux-hwe-6.2 Package: linux-hwe-6.5 Package: linux-hwe-6.8 Package: linux-hwe-edge Package: linux-ibm Package: linux-ibm-5.15 Package: linux-ibm-5.4 Package: linux-ibm-6.8 Package: linux-intel-5.13 Package: linux-intel-iot-realtime Package: linux-intel-iotg Package: linux-intel-iotg-5.15 Package: linux-iot Package: linux-kvm Package: linux-lowlatency Package: linux-lowlatency-hwe-5.15 Package: linux-lowlatency-hwe-5.19 Package: linux-lowlatency-hwe-6.11 Package: linux-lowlatency-hwe-6.2 Package: linux-lowlatency-hwe-6.5 Package: linux-lowlatency-hwe-6.8 Package: linux-nvidia Package: linux-nvidia-6.11 Package: linux-nvidia-6.17 Package: linux-nvidia-6.2 Package: linux-nvidia-6.5 Package: linux-nvidia-6.8 Package: linux-nvidia-lowlatency Package: linux-nvidia-tegra Package: linux-nvidia-tegra-5.15 Package: linux-nvidia-tegra-igx Package: linux-oem Package: linux-oem-5.10 Package: linux-oem-5.13 Package: linux-oem-5.14 Package: linux-oem-5.17 Package: linux-oem-5.6 Package: linux-oem-6.0 Package: linux-oem-6.1 Package: linux-oem-6.11 Package: linux-oem-6.14 Package: linux-oem-6.17 Package: linux-oem-6.5 Package: linux-oem-6.8 Package: linux-oracle Package: linux-oracle-5.0 Package: linux-oracle-5.11 Package: linux-oracle-5.13 Package: linux-oracle-5.15 Package: linux-oracle-5.3 Package: linux-oracle-5.4 Package: linux-oracle-5.8 Package: linux-oracle-6.14 Package: linux-oracle-6.17 Package: linux-oracle-6.5 Package: linux-oracle-6.8 Package: linux-raspi Package: linux-raspi-5.4 Package: linux-raspi-realtime Package: linux-raspi2 Package: linux-realtime Package: linux-realtime-6.14 Package: linux-realtime-6.17 Package: linux-realtime-6.8 Package: linux-riscv Package: linux-riscv-5.11 Package: linux-riscv-5.15 Package: linux-riscv-5.19 Package: linux-riscv-5.8 Package: linux-riscv-6.14 Package: linux-riscv-6.17 Package: linux-riscv-6.5 Package: linux-riscv-6.8 Package: linux-starfive-5.19 Package: linux-starfive-6.2 Package: linux-starfive-6.5 Package: linux-vmware Package: linux-xilinx Package: linux-xilinx-zynqmp Platform: Linux Ecosystem: Azure Linux Ecosystem: Debian Ecosystem: Ubuntu

Description

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

timers: Fix NULL function pointer race in timer_shutdown_sync()

There is a race condition between timer_shutdown_sync() and timer
expiration that can lead to hitting a WARN_ON in expire_timers().

The issue occurs when timer_shutdown_sync() clears the timer function
to NULL while the timer is still running on another CPU. The race
scenario looks like this:

CPU0 CPU1
<SOFTIRQ>
lock_timer_base()
expire_timers()
base->running_timer = timer;
unlock_timer_base()
[call_timer_fn enter]
mod_timer()
...
timer_shutdown_sync()
lock_timer_base()
// For now, will not detach the timer but only clear its function to NULL
if (base->running_timer != timer)
ret = detach_if_pending(timer, base, true);
if (shutdown)
timer->function = NULL;
unlock_timer_base()
[call_timer_fn exit]
lock_timer_base()
base->running_timer = NULL;
unlock_timer_base()
...
// Now timer is pending while its function set to NULL.
// next timer trigger
<SOFTIRQ>
expire_timers()
WARN_ON_ONCE(!fn) // hit
...
lock_timer_base()
// Now timer will detach
if (base->running_timer != timer)
ret = detach_if_pending(timer, base, true);
if (shutdown)
timer->function = NULL;
unlock_timer_base()

The problem is that timer_shutdown_sync() clears the timer function
regardless of whether the timer is currently running. This can leave a
pending timer with a NULL function pointer, which triggers the
WARN_ON_ONCE(!fn) check in expire_timers().

Fix this by only clearing the timer function when actually detaching the
timer. If the timer is running, leave the function pointer intact, which is
safe because the timer will be properly detached when it finishes running.

Affected products

VendorProductAffectedFixed
Linux Linux 6.1.158 – < 6.1.159, 6.2 6.1.159

Fixed in Linux distributions

Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.

ReleasePackageFixed inAdvisory
Debian 14 linux 6.17.10-1 —
Debian 13 linux 6.12.63-1 —
Debian 12 linux 6.1.159-1 —
Debian 11 linux-6.1 6.1.159-1~deb11u1 DLA-4436-1
ReleasePackageFixed inAdvisory
Ubuntu Nvidia-BlueField 24.04 LTS linux-bluefield 6.8.0-1017.21 —
Ubuntu Nvidia-BlueField 22.04 LTS linux-bluefield 5.15.0-1095.97 —
Ubuntu 25.10 linux 6.17.0-19.19 USN-8094-1
Ubuntu 25.10 linux-aws +2 6.17.0-1009.9 USN-8094-1
Ubuntu 25.10 linux-azure +1 6.17.0-1010.10 USN-8094-5, USN-8094-4
Ubuntu 25.10 linux-azure-fde No fix yet —
Ubuntu 25.10 linux-realtime 6.17.0-1008.9 USN-8094-2
Ubuntu 25.10 linux-riscv 6.17.0-19.19.1 —
Ubuntu 24.04 LTS linux 6.8.0-106.106 USN-8095-1
Ubuntu 24.04 LTS linux-aws 6.8.0-1050.53 USN-8095-1
Ubuntu 24.04 LTS linux-aws-6.17 6.17.0-1009.9~24.04.2 USN-8094-1
Ubuntu 24.04 LTS linux-azure 6.8.0-1051.57 USN-8125-1
Ubuntu 24.04 LTS linux-azure-6.17 6.17.0-1010.10~24.04.1 USN-8094-4
Ubuntu 24.04 LTS linux-azure-fde 6.8.0-1058.65 —
Ubuntu 24.04 LTS linux-azure-nvidia 6.8.0-1039.42 —
Ubuntu 24.04 LTS linux-gcp 6.8.0-1052.55 USN-8095-1
Ubuntu 24.04 LTS linux-gcp-6.17 6.17.0-1009.9~24.04.3 USN-8094-2
Ubuntu 24.04 LTS linux-gke 6.8.0-1048.53 USN-8095-1
Ubuntu 24.04 LTS linux-gkeop 6.8.0-1035.38 USN-8095-1
Ubuntu 24.04 LTS linux-hwe-6.17 6.17.0-19.19~24.04.2 USN-8094-1
Ubuntu 24.04 LTS linux-ibm 6.8.0-1049.49 USN-8095-1
Ubuntu 24.04 LTS linux-lowlatency 6.8.0-106.106.1 USN-8095-1
Ubuntu 24.04 LTS linux-nvidia 6.8.0-1049.52 USN-8100-1
Ubuntu 24.04 LTS linux-nvidia-6.17 6.17.0-1018.18 —
Ubuntu 24.04 LTS linux-nvidia-lowlatency 6.8.0-1049.52.1 USN-8100-1
Ubuntu 24.04 LTS linux-nvidia-tegra 6.8.0-1020.20 —
Ubuntu 24.04 LTS linux-oem-6.17 6.17.0-1017.17 USN-8152-1
Ubuntu 24.04 LTS linux-oracle 6.8.0-1047.48 USN-8095-1
Ubuntu 24.04 LTS linux-oracle-6.17 6.17.0-1009.9~24.04.1 USN-8094-1
Ubuntu 24.04 LTS linux-raspi 6.8.0-1050.54 USN-8095-5
Ubuntu 24.04 LTS linux-riscv +18 No fix yet —
Ubuntu 24.04 LTS linux-riscv-6.17 6.17.0-19.19.1~24.04.1 —
Ubuntu 24.04 LTS linux-xilinx 6.8.0-1028.29 USN-8261-1
Ubuntu 22.04 LTS linux 5.15.0-185.195 USN-8493-1
Ubuntu 22.04 LTS linux-aws 5.15.0-1111.118 USN-8493-1
Ubuntu 22.04 LTS linux-aws-6.8 6.8.0-1050.53~22.04.1 USN-8095-4
Ubuntu 22.04 LTS linux-azure +1 5.15.0-1116.125 USN-8493-1
Ubuntu 22.04 LTS linux-azure-6.8 6.8.0-1051.57~22.04.1 USN-8126-1
Ubuntu 22.04 LTS linux-azure-fde-6.8 6.8.0-1058.65~22.04.1 —
Ubuntu 22.04 LTS linux-gcp 5.15.0-1111.121 USN-8493-1
Ubuntu 22.04 LTS linux-gcp-6.8 6.8.0-1052.55~22.04.1 USN-8095-1
Ubuntu 22.04 LTS linux-gke 5.15.0-1107.113 USN-8493-1
Ubuntu 22.04 LTS linux-gkeop 5.15.0-1094.102 USN-8493-1
Ubuntu 22.04 LTS linux-hwe-6.8 +1 6.8.0-106.106~22.04.1 USN-8095-1
Ubuntu 22.04 LTS linux-ibm 5.15.0-1105.109 USN-8493-1
Ubuntu 22.04 LTS linux-ibm-6.8 6.8.0-1049.49~22.04.1 USN-8095-1
Ubuntu 22.04 LTS linux-intel-iotg 5.15.0-1106.112 USN-8493-1
Ubuntu 22.04 LTS linux-kvm 5.15.0-1103.108 USN-8493-1
Ubuntu 22.04 LTS linux-lowlatency 5.15.0-183.193 USN-8493-1
Ubuntu 22.04 LTS linux-lowlatency-hwe-6.8 6.8.0-106.106.1~22.04.1 USN-8095-1
Ubuntu 22.04 LTS linux-nvidia 5.15.0-1106.107 USN-8493-1
Ubuntu 22.04 LTS linux-nvidia-6.8 6.8.0-1049.52~22.04.1 USN-8100-1
Ubuntu 22.04 LTS linux-nvidia-tegra 5.15.0-1063.63 USN-8493-1
Ubuntu 22.04 LTS linux-nvidia-tegra-igx 5.15.0-1052.52 USN-8493-1
Ubuntu 22.04 LTS linux-oracle 5.15.0-1108.114 USN-8493-1
Ubuntu 22.04 LTS linux-oracle-6.8 6.8.0-1047.48~22.04.1 USN-8095-1
Ubuntu 22.04 LTS linux-raspi 5.15.0-1105.108 USN-8527-1
Ubuntu 22.04 LTS linux-riscv +32 No fix yet —
Ubuntu 22.04 LTS linux-xilinx-zynqmp 5.15.0-1074.78 USN-8528-1
Show 10 more (older releases, extended support, other products)
ReleasePackageFixed inAdvisory
Ubuntu 20.04 LTS linux-gke +28 No fix yet —
Ubuntu 18.04 LTS linux-gcp +14 No fix yet —
Ubuntu 16.04 LTS linux-hwe-edge No fix yet —
Ubuntu Pro Realtime 24.04 LTS linux-raspi-realtime 6.8.0-2040.41 USN-8095-5
Ubuntu Pro Realtime 24.04 LTS linux-realtime 6.8.1-1045.46 USN-8095-3
Ubuntu Pro Realtime 24.04 LTS linux-realtime-6.14 No fix yet —
Ubuntu Pro Realtime 24.04 LTS linux-realtime-6.17 6.17.0-1008.9~24.04.1 USN-8094-3
Ubuntu Pro Realtime 22.04 LTS linux-intel-iot-realtime 5.15.0-1103.105 USN-8493-1
Ubuntu Pro Realtime 22.04 LTS linux-realtime 5.15.0-1110.119 USN-8493-1
Ubuntu Pro Realtime 22.04 LTS linux-realtime-6.8 6.8.1-1045.46~22.04.1 USN-8095-3
Ubuntu Pro FIPS-updates 24.04 LTS linux-aws-fips 6.8.0-1050.53+fips1 USN-8095-2
Ubuntu Pro FIPS-updates 24.04 LTS linux-azure-fips 6.8.0-1052.58+fips1 USN-8165-1
Ubuntu Pro FIPS-updates 24.04 LTS linux-fips 6.8.0-106.106+fips1 USN-8095-2
Ubuntu Pro FIPS-updates 24.04 LTS linux-gcp-fips 6.8.0-1052.55+fips1 USN-8095-2
Ubuntu Pro FIPS-updates 22.04 LTS linux-aws-fips 5.15.0-1111.118+fips1 USN-8493-1
Ubuntu Pro FIPS-updates 22.04 LTS linux-azure-fips 5.15.0-1116.125+fips1 USN-8547-2
Ubuntu Pro FIPS-updates 22.04 LTS linux-fips 5.15.0-185.195+fips1 USN-8493-1
Ubuntu Pro FIPS-updates 22.04 LTS linux-gcp-fips 5.15.0-1111.121+fips1 USN-8493-1
Ubuntu Pro FIPS-updates 20.04 LTS linux-fips +3 No fix yet —
Ubuntu Pro 20.04 LTS linux +10 No fix yet —
Ubuntu Pro 20.04 LTS linux-aws-5.15 5.15.0-1111.118~20.04.1 USN-8493-1
Ubuntu Pro 20.04 LTS linux-azure-5.15 +1 5.15.0-1116.125~20.04.1 USN-8493-1
Ubuntu Pro 20.04 LTS linux-gcp-5.15 5.15.0-1111.121~20.04.1 USN-8547-1
Ubuntu Pro 20.04 LTS linux-hwe-5.15 5.15.0-185.195~20.04.1 USN-8493-1
Ubuntu Pro 20.04 LTS linux-ibm-5.15 +1 5.15.0-1105.109~20.04.1 USN-8493-1
Ubuntu Pro 20.04 LTS linux-intel-iotg-5.15 5.15.0-1106.112~20.04.1 USN-8547-1
Ubuntu Pro 20.04 LTS linux-lowlatency-hwe-5.15 5.15.0-183.193~20.04.1 USN-8493-1
Ubuntu Pro 20.04 LTS linux-nvidia-tegra-5.15 5.15.0-1063.63~20.04.1 USN-8493-1
Ubuntu Pro 20.04 LTS linux-oracle-5.15 5.15.0-1108.114~20.04.1 USN-8493-2
Ubuntu Pro 18.04 LTS linux-aws-5.4 +6 No fix yet —
ReleasePackageFixed inAdvisory
RHEL 10 rv +76 6.12.0-211.43.1.el10_2 RHSA-2026:49871
RHEL 9 rv +75 5.14.0-687.34.1.el9_8 RHSA-2026:49870

AlmaLinux

Errata ↗
ReleasePackageFixed inAdvisory
AlmaLinux 10 rv +74 6.12.0-211.43.1.el10_2 ALSA-2026:49871
AlmaLinux 9 rv +73 5.14.0-687.34.1.el9_8 ALSA-2026:49870

Rocky Linux

Errata ↗
ReleasePackageFixed inAdvisory
Rocky Linux 10 kernel 6.12.0-211.43.1.el10_2 RLSA-2026:49871
Rocky Linux 9 kernel 5.14.0-687.34.1.el9_8 RXSA-2026:49870, RLSA-2026:49870
ReleasePackageFixed inAdvisory
SLES 15 SP7 kernel-64kb +7 6.4.0-150700.53.81.1 SUSE-SU-2026:4254-1
SLES 15 SP7 kernel-default-base 6.4.0-150700.53.81.1.150700.17.45.1 SUSE-SU-2026:4254-1
SLES 15 SP6 kernel-64kb +6 6.4.0-150600.23.135.1 SUSE-SU-2026:4369-1
SLES 15 SP6 kernel-default-base 6.4.0-150600.23.135.1.150600.12.62.4 SUSE-SU-2026:4369-1
SLES 12 SP5 kernel-syms +2 4.12.14-122.328.1 SUSE-SU-2026:4282-1
Show 10 more (older releases, extended support, other products)
ReleasePackageFixed inAdvisory
SLES for SAP 16.0 kernel-64kb +8 6.12.0-160000.38.1 SUSE-SU-2026:23902-1
SLES for SAP 16.0 kernel-default-base 6.12.0-160000.38.1.160000.2.23 SUSE-SU-2026:23902-1
SLES for SAP 15 SP6 kernel-default-base 6.4.0-150600.23.135.1.150600.12.62.4 SUSE-SU-2026:4369-1
SLES for SAP 15 SP6 kernel-docs +4 6.4.0-150600.23.135.1 SUSE-SU-2026:4369-1
SLES 16.0 kernel-64kb +8 6.12.0-160000.38.1 SUSE-SU-2026:23902-1, SUSE-SU-2026:23897-1
SLES 16.0 kernel-default-base 6.12.0-160000.38.1.160000.2.23 SUSE-SU-2026:23902-1
SLE Micro 6.2 kernel-default-base 6.12.0-160000.38.1.160000.2.23 SUSE-SU-2026:23887-1
SLE Micro 6.2 kernel-rt +5 6.12.0-160000.38.1 SUSE-SU-2026:23887-1, SUSE-SU-2026:23881-1
SLE Micro 6.1 kernel-default-base 6.4.0-52.1.21.34 SUSE-SU-2026:23529-1
SLE Micro 6.1 kernel-rt +4 6.4.0-52.1 SUSE-SU-2026:23529-1, SUSE-SU-2026:23528-1
SLE Micro 6.0 kernel-default-base 6.4.0-52.1.21.36 SUSE-SU-2026:23481-1
SLE Micro 6.0 kernel-rt +4 6.4.0-52.1 SUSE-SU-2026:23481-1, SUSE-SU-2026:23477-1
SLE Live Patching 15 SP7 kernel-default 6.4.0-150700.53.81.1 SUSE-SU-2026:4254-1
SLE Live Patching 15 SP7 kernel-livepatch-SLE15-SP7-RT_Update_20 1-150700.1.3.1 SUSE-SU-2026:4120-1
SLE Live Patching 15 SP7 kernel-livepatch-SLE15-SP7_Update_21 1-150700.15.3.1 SUSE-SU-2026:4254-1
SLE Live Patching 15 SP6 kernel-default 6.4.0-150600.23.135.1 SUSE-SU-2026:4369-1
SLE Live Patching 15 SP6 kernel-livepatch-SLE15-SP6_Update_31 1-150600.13.3.4 SUSE-SU-2026:4369-1
SLE Live Patching 12 SP5 kernel-default 4.12.14-122.328.1 SUSE-SU-2026:4282-1
SLE Live Patching 12 SP5 kgraft-patch-SLE12-SP5_Update_87 1-8.5.1 SUSE-SU-2026:4282-1
SUSE Real Time Module 15 SP7 kernel-rt +2 6.4.0-150700.7.75.1 SUSE-SU-2026:4120-1
ReleasePackageFixed inAdvisory
openSUSE Leap 16.0 kernel-default-base 6.12.0-160000.38.1.160000.2.22 openSUSE-SU-2026:21910-1
openSUSE Leap 16.0 kernel-rt +11 6.12.0-160000.38.1 openSUSE-SU-2026:21910-1

Amazon Linux

ReleasePackageFixed inAdvisory
Amazon Linux 2023 kernel-livepatch-6.12.63-84.121 +1 1:1.0-0.amzn2023 ALAS2023-2026-1430, ALAS2023-2025-1350
Amazon Linux 2023 perf +14 1:6.1.159-181.297.amzn2023 ALAS2023-2025-1350
Amazon Linux 2023 perf6.12 +14 1:6.12.63-84.121.amzn2023 ALAS2023-2026-1430

Azure Linux

ReleasePackageFixed inAdvisory
Azure Linux 3 kernel 6.6.119.3-1 —

Oracle Linux

ReleasePackageFixed inAdvisory
Oracle Linux 10 rv +29 6.12.0-211.43.1.el10_2 ELSA-2026-49871
Oracle Linux 9 kernel-uek +34 6.12.0-108.64.6.3.el10uek ELSA-2026-50112
Oracle Linux 9 rv +28 5.14.0-687.34.1.el9_8 ELSA-2026-49870

Advisories 50

References