CVE-2026-89520 sched/core: Make core-sched flips wait for in-flight selections
A race condition in the Linux kernel core scheduler allows lock state corruption, potentially leading to system crashes or privilege escalation.
- 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-2026-89520?
CVE-2026-89520 is a high-severity vulnerability in Linux, published on 11 Sep 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:
sched/core: Make core-sched flips wait for in-flight selections
Core scheduling's pick_next_task() operates on all sibling rqs under one acquisition of the shared core-wide lock. A ->pick_task() that releases the rq lock leaves every sibling __lock momentarily free, letting __sched_core_flip(false) complete mid-selection and rebind rq_lockp() under it. The selection resumes on the split locks, touching sibling state it no longer protects, and __schedule() finally releases a lock that was never taken while leaking the one that was.
Count in-flight core-wide selections in the leader's rq->core_pick_in_flight and make __sched_core_flip() wait for the count to drain. The count only changes under the shared lock, which the flip holds while sampling, so no other ordering is needed. The wait can repeat while selections overlap, but the flip backs off between samples and flips are rare cookie-lifetime events.
sched_core_cpu_deactivate() moves the count to the new leader - a stale copy left behind would bias it forever if that CPU later returns as its own leader.
Which versions are affected by CVE-2026-89520?
How do I fix CVE-2026-89520?
Apply the vendor's patch.
Is CVE-2026-89520 being exploited?
There is no known exploitation of CVE-2026-89520 in the wild and no public exploit code.
Sources
Also known as AZL-100676, BELL-CVE-2026-89520, DEBIAN-CVE-2026-89520, GHSA-q4pw-m5gm-wg9r, UBUNTU-CVE-2026-89520.