# 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.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Jun 2026
- **Updated:** 15 Oct 2026
- **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, ROOT-OS-UBUNTU-2204-CVE-2026-53198, ROOT-OS-UBUNTU-2404-CVE-2026-53198, UBUNTU-CVE-2026-53198

## 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 (Use After Free)

## Which versions are affected by CVE-2026-53198?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-53198?

Apply the vendor's patch.

## 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

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-53198 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-53198 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-53198/ (Markdown: https://insights.sbomify.com/CVE-2026-53198/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53198
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53198
- OSV: https://osv.dev/vulnerability/CVE-2026-53198

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53198/
Summaries are generated and may contain mistakes; the official description above is the record.