CVE-2026-68421 sched_ext: Don't warn on core-sched forced idle in put_prev_task_scx()
A logic error in the Linux kernel scheduler causes false warnings during core scheduling, potentially leading to system instability or denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-68421?
CVE-2026-68421 is a denial of service vulnerability in Linux, published on 10 Aug 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_ext: Don't warn on core-sched forced idle in put_prev_task_scx()
put_prev_task_scx() warns when a runnable task drops to a lower sched_class without SCX_OPS_ENQ_LAST, on the assumption that balance_one() would have kept it running. Core scheduling breaks that: a forced-idle SMT sibling reschedules through the core_pick fast path in pick_next_task(), which skips pick_task_scx() and thus balance_one(), so a runnable task can drop to idle with ENQ_LAST unset.
Gate the warning on sched_cpu_cookie_match(): a cookie mismatch means core scheduling forced the idle, while a match (or core scheduling off) still catches a genuine missing-ENQ_LAST drop.
Which versions are affected by CVE-2026-68421?
How do I fix CVE-2026-68421?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-68421 being exploited?
There is no known exploitation of CVE-2026-68421 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-68421, DEBIAN-CVE-2026-68421, GHSA-wg3q-w98j-244c, UBUNTU-CVE-2026-68421.