CVE-2026-53198 ksmbd: fix use-after-free of a deferred file_lock on double SMB2_CANCEL
An authenticated SMB client can trigger a use-after-free in the Linux kernel ksmbd module via double SMB2_CANCEL requests, potentially leading to code execution or privilege escalation.
- 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-2026-53198?
CVE-2026-53198 is a high-severity use after free vulnerability in Linux kernel, published on 25 Jun 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: fix use-after-free of a deferred file_lock on double SMB2_CANCEL
A deferred byte-range lock (an SMB2_LOCK that blocks) registers an async work on conn->async_requests via setup_async_work(), with cancel_fn = smb2_remove_blocked_lock and cancel_argv[0] pointing at the struct file_lock.
When the request is cancelled, the worker frees the file_lock with locks_free_lock() and takes the cancelled early-exit, which "goto out"s and never reaches release_async_work() -- the only site that unlinks the work from conn->async_requests and clears cancel_fn/cancel_argv. The work therefore stays matchable on async_requests with a live cancel_fn pointing at the freed file_lock, until connection teardown finally runs release_async_work().
smb2_cancel() fires cancel_fn unconditionally with no state guard, so a second SMB2_CANCEL for the same AsyncId, arriving in that window, re-runs smb2_remove_blocked_lock() on the freed file_lock -- a slab use-after-free:
BUG: KASAN: slab-use-after-free in __locks_delete_block __locks_delete_block locks_delete_block ksmbd_vfs_posix_lock_unblock smb2_remove_blocked_lock smb2_cancel <- 2nd SMB2_CANCEL fires cancel_fn handle_ksmbd_work Allocated by ...: locks_alloc_lock <- smb2_lock Freed by ...: locks_free_lock <- smb2_lock (cancelled branch) ... cache file_lock_cache of size 192
Reproduced on mainline with KASAN by an authenticated SMB client.
Skip a work whose state is already KSMBD_WORK_CANCELLED so its cancel callback cannot be fired a second time.
Weakness: CWE-416
Which versions are affected by CVE-2026-53198?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-53198?
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-2026-53198 being exploited?
There is no known exploitation of CVE-2026-53198 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-90336, BELL-CVE-2026-53198, DEBIAN-CVE-2026-53198, GHSA-62m5-m548-5v5f, ROOT-OS-DEBIAN-11-CVE-2026-53198, ROOT-OS-DEBIAN-12-CVE-2026-53198 and 3 more.