CVE-2025-68214: Linux kernel · timers: Fix NULL function pointer race in timer_shutdown_sync()
Affects Linux kernelSource CVE Database V5
Not known to be exploited · fixed in ba43ac025c4318241f8edf94f31d2eebab86991b : update Linux kernel when convenient.
Data as of 5 Nov 2026, 21:34 UTC
Rated by Threat Radar · No CVSS score from NVD or the CNA
Thin evidence
One scorer or none- CISA SSVC
- Exploitation
- No evidence of active exploitation and no public proof of concept
- Automatable
- Attackers cannot reliably automate steps 1–4 of the kill chain
- Technical impact
- Limited control over the software or limited information exposure
CISA SSVC assessment, 2026-11-05.
- Patch
- Available – fixed in ba43ac025c4318241f8edf94f31d2eebab86991b, a01efa7a780c42ac5170a949bd95c9786ffcc60a, 176725f4848376530a0f0da9023f956afcc33585 +4
Exploitation evidence
Disclosed: evidence found.
CVE published 16 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
|
| LinuxLinux | Affected
| Fixed in– |
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.
References
- git.kernel.org/stable/c/ba43ac025c4318241f8edf94f31d2eebab86991b (opens in a new tab)
- git.kernel.org/stable/c/1a975716cc8977f461e45e28e3e5977d46ad7a6a (opens in a new tab)
- git.kernel.org/stable/c/6665fbd7730b26d770c232b20d1b907e6a67a914 (opens in a new tab)
- git.kernel.org/stable/c/176725f4848376530a0f0da9023f956afcc33585 (opens in a new tab)
- git.kernel.org/stable/c/a01efa7a780c42ac5170a949bd95c9786ffcc60a (opens in a new tab)
- git.kernel.org/stable/c/20739af07383e6eb1ec59dcd70b72ebfa9ac362c (opens in a new tab)