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CVE-2025-38352 A-425282960 ASB-A-425282960

posix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del()

High Known exploited Linux
Severity
7.8 / 10
High · CVSS 3.1
Exploit chance (EPSS)
1.36%
Chance of exploitation in the next 30 days. Higher than 71.67% of scored vulnerabilities.
Known exploited
Yes
In CISA's catalog since Sep 4, 2025
Weakness
CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition
Fix
6.15.3
Upgrade Kernel to this version or later
Exploited in the wild. Linux Kernel Time-of-Check Time-of-Use (TOCTOU) Race Condition Vulnerability (Linux Kernel). Required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Due for U.S. federal agencies by Sep 25, 2025.

Description

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

posix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del()

If an exiting non-autoreaping task has already passed exit_notify() and calls handle_posix_cpu_timers() from IRQ, it can be reaped by its parent or debugger right after unlock_task_sighand().

If a concurrent posix_cpu_timer_del() runs at that moment, it won't be able to detect timer->it.cpu.firing != 0: cpu_timer_task_rcu() and/or lock_task_sighand() will fail.

Add the tsk->exit_state check into run_posix_cpu_timers() to fix this.

This fix is not needed if CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y, because exit_task_work() is called before exit_notify(). But the check still makes sense, task_work_add(&tsk->posix_cputimers_work.work) will fail anyway in this case.

Affected versions

Linux

PackageVulnerableFixed in
Kernel
>= 2.6.36, < 5.4.295
>= 5.5.0, < 5.10.239
>= 5.11.0, < 5.15.186
>= 5.16.0, < 6.1.142
>= 6.2.0, < 6.6.94
>= 6.7.0, < 6.12.34
>= 6.13.0, < 6.15.3
5.4.295
5.10.239
5.15.186
6.1.142
6.6.94
6.12.34
6.15.3

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

Kernel Linux → 6.15.3

Set Kernel to 6.15.3 or later in your manifest.

Severity breakdown

CVSS 3.1 7.8

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

Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Weakness

CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition

The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.

How to prevent it
  • Implementation: The most basic advice for TOCTOU vulnerabilities is to not perform a check before the use. This does not resolve the underlying issue of the execution of a function on a resource whose state and identity cannot be assured, but it does help to limit the false sense of security given by the check.
  • Implementation: When the file being altered is owned by the current user and group, set the effective gid and uid to that of the current user and group when executing this statement.
  • Architecture and Design: Limit the interleaving of operations on files from multiple processes.
  • Implementation, Architecture and Design: If you cannot perform operations atomically and you must share access to the resource between multiple processes or threads, then try to limit the amount of time (CPU cycles) between the check and use of the resource. This will not fix the problem, but it could make it more difficult for an attack to succeed.
  • Implementation: Recheck the resource after the use call to verify that the action was taken appropriately.
  • Architecture and Design: Ensure that some environmental locking mechanism can be used to protect resources effectively.
  • Implementation: Ensure that locking occurs before the check, as opposed to afterwards, such that the resource, as checked, is the same as it is when in use.

References

Advisories

Exploits and evidence

Packages

Other links

Timeline

  1. Published
  2. Added to CISA's Known Exploited Vulnerabilities catalog
  3. Remediation due for U.S. federal agencies
  4. Last updated by the source
  5. Latest EPSS score
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