CVE-2026-90155 ksmbd: detach blocked lock requests before freeing
A use-after-free vulnerability in the Linux kernel's ksmbd module allows attackers to cause a denial of service or potentially execute code via crafted lock requests.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90155?
CVE-2026-90155 is an use after free vulnerability in Linux, published on 17 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: detach blocked lock requests before freeing
A file_lock retained by ksmbd for byte-range lock bookkeeping can still be part of the VFS blocked-request graph. In particular, the VFS can chain a new waiter below an already blocked request through flc_blocked_requests. The ksmbd_file reference count does not cover that graph.
Both __ksmbd_close_fd() and the cross-request unlock path free these retained file_lock objects directly. If a dependent waiter is still attached, locks_release_private() hits BUG_ON(!list_empty(&flc->flc_blocked_requests)). The same lifetime mismatch can leave a freed ksmbd_lock reachable through its request-local llist.
Detach the file_lock from the blocked-request graph before freeing it in the close, cross-request unlock, and rollback paths. locks_delete_block() also wakes requests chained below the object. Remove llist when a completed lock is published so a globally visible ksmbd_lock no longer points into the submitting worker's stack.
Which versions are affected by CVE-2026-90155?
How do I fix CVE-2026-90155?
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-2026-90155 being exploited?
There is no known exploitation of CVE-2026-90155 in the wild and no public exploit code.
Sources
Also known as AZL-102578, BELL-CVE-2026-90155, DEBIAN-CVE-2026-90155, GHSA-52g3-8w7f-v5w2, UBUNTU-CVE-2026-90155.