CVE-2026-98258 posix-cpu-timers: Prevent freeing a timer which is queued on the expiry list
A race condition in Linux kernel POSIX CPU timers allows use-after-free, potentially enabling local attackers to execute code or escalate privileges.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-98258?
CVE-2026-98258 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
posix-cpu-timers: Prevent freeing a timer which is queued on the expiry list
Kijo analyzed another race in the POSIX CPU timer code:
Commit bf635681c906 converted cpu_timer::firing from a tristate value to a boolean. This lost the distinction between "not owned by the firing list" and "still owned, but delivery was canceled". The resulting race is:
expiry handler timer_settime() timer_delete() -------------- --------------- -------------- collect timer onto private firing list firing = true observes firing = true firing = false return TIMER_RETRY wait for handler observes firing = false finish deletion unhash and free timer resume list traversal read freed elist.next -> UAF
The firing bit is clearly the wrong indicator since that commit.
Check whether the timer is queued on the expiry list or not instead. If it is queued clear the firing bit to prevent signal delivery as before and return TIMER_RETRY so the caller unlocks the timer which allows the expiry code to make progress and remove it from the list.
Which versions are affected by CVE-2026-98258?
How do I fix CVE-2026-98258?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-98258 being exploited?
There is no known exploitation of CVE-2026-98258 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-98258, DEBIAN-CVE-2026-98258, GHSA-h9hq-jmqv-hjx4, UBUNTU-CVE-2026-98258.