CVE-2025-21786: workqueue: Put the pwq after detaching the rescuer from the pool

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-02-27 · updated 2026-06-17
Weakness: CWE-416

Description

In the Linux kernel, the following vulnerability has been resolved: workqueue: Put the pwq after detaching the rescuer from the pool The commit 68f83057b913("workqueue: Reap workers via kthread_stop() and remove detach_completion") adds code to reap the normal workers but mistakenly does not handle the rescuer and also removes the code waiting for the rescuer in put_unbound_pool(), which caused a use-after-free bug reported by Cheung Wall. To avoid the use-after-free bug, the pool’s reference must be held until the detachment is complete. Therefore, move the code that puts the pwq after detaching the rescuer from the pool.

Affected products

Linux kernel: before 6.12.16; from 6.13 before 6.13.4 — fixed in 6.12.16, 6.13.4

How to fix

Upgrade to a fixed version: Linux kernel 6.12.16, 6.13.4. Check the vendor advisory for mitigations.

References

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