CVE-2026-90276 md/md-llbitmap: stop daemon timer rearm on destroy
A use-after-free vulnerability in the Linux kernel's md/llbitmap module allows attackers to cause a denial of service or potentially execute code during device teardown.
- 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-2026-90276?
CVE-2026-90276 is an use after free vulnerability in Linux, published on 17 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:
md/md-llbitmap: stop daemon timer rearm on destroy
llbitmap_destroy() deletes pending_timer before flushing md_llbitmap_io_wq. However, daemon_work can still be queued or running after the timer has been deleted, and the daemon path can arm pending_timer again when it finds dirty chunks that are not ready to flush yet.
If that happens during teardown, pending_timer can remain armed after llbitmap is freed and later dereference freed memory.
Add a BITMAP_SHUTDOWN bit to llbitmap->flags, set it before deleting the timer, and make the timer and daemon paths stop queueing or rearming work once teardown starts. Cancel daemon_work before flushing the shared workqueue so no already queued daemon instance can race with the free. Use timer_shutdown_sync() so a daemon instance that passed the shutdown check before teardown cannot rearm the timer afterward.
BITMAP_SHUTDOWN is a runtime-only state. Mask it out when reading and updating the llbitmap superblock so the shutdown state is never loaded from disk or persisted to disk.
Which versions are affected by CVE-2026-90276?
How do I fix CVE-2026-90276?
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-2026-90276 being exploited?
There is no known exploitation of CVE-2026-90276 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-90276, DEBIAN-CVE-2026-90276, GHSA-wg47-q44p-vcm3, UBUNTU-CVE-2026-90276.