CVE-2026-23371 sched/deadline: Fix missing ENQUEUE_REPLENISH during PI de-boosting

Medium 5.5 Published 25 Mar 2026 Updated 21 Oct 2026

A logic error in the Linux kernel's deadline scheduler can cause bandwidth accounting corruption and system warnings, potentially leading to denial of service.

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-2026-23371?

CVE-2026-23371 is a medium-severity denial of service vulnerability in Linux kernel, published on 25 Mar 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/deadline: Fix missing ENQUEUE_REPLENISH during PI de-boosting

Running stress-ng --schedpolicy 0 on an RT kernel on a big machine might lead to the following WARNINGs (edited).

sched: DL de-boosted task PID 22725: REPLENISH flag missing

WARNING: CPU: 93 PID: 0 at kernel/sched/deadline.c:239 dequeue_task_dl+0x15c/0x1f8 ... (running_bw underflow) Call trace: dequeue_task_dl+0x15c/0x1f8 (P) dequeue_task+0x80/0x168 deactivate_task+0x24/0x50 push_dl_task+0x264/0x2e0 dl_task_timer+0x1b0/0x228 __hrtimer_run_queues+0x188/0x378 hrtimer_interrupt+0xfc/0x260 ...

The problem is that when a SCHED_DEADLINE task (lock holder) is changed to a lower priority class via sched_setscheduler(), it may fail to properly inherit the parameters of potential DEADLINE donors if it didn't already inherit them in the past (shorter deadline than donor's at that time). This might lead to bandwidth accounting corruption, as enqueue_task_dl() won't recognize the lock holder as boosted.

The scenario occurs when: 1. A DEADLINE task (donor) blocks on a PI mutex held by another DEADLINE task (holder), but the holder doesn't inherit parameters (e.g., it already has a shorter deadline) 2. sched_setscheduler() changes the holder from DEADLINE to a lower class while still holding the mutex 3. The holder should now inherit DEADLINE parameters from the donor and be enqueued with ENQUEUE_REPLENISH, but this doesn't happen

Fix the issue by introducing __setscheduler_dl_pi(), which detects when a DEADLINE (proper or boosted) task gets setscheduled to a lower priority class. In case, the function makes the task inherit DEADLINE parameters of the donoer (pi_se) and sets ENQUEUE_REPLENISH flag to ensure proper bandwidth accounting during the next enqueue operation.

Which versions are affected by CVE-2026-23371?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-23371?

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-2026-23371 being exploited?

There is no known exploitation of CVE-2026-23371 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as AZL-80663, BELL-CVE-2026-23371, DEBIAN-CVE-2026-23371, GHSA-55fv-ccjv-2hr3, ROOT-OS-DEBIAN-11-CVE-2026-23371, ROOT-OS-DEBIAN-12-CVE-2026-23371 and 4 more.