# CVE-2026-64437: ksmbd: fix use-after-free of a deferred file_lock on SMB2_CLOSE then SMB2_CANCEL

> An authenticated SMB client can trigger a use-after-free in the Linux kernel ksmbd module via specific SMB2 commands, 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 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-64437, DEBIAN-CVE-2026-64437, GHSA-x5p7-hg5v-9p54, ROOT-OS-DEBIAN-12-CVE-2026-64437, ROOT-OS-UBUNTU-2204-CVE-2026-64437, UBUNTU-CVE-2026-64437

## What is CVE-2026-64437?

CVE-2026-64437 is a high-severity use after free vulnerability in Linux kernel, published on 25 Jul 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 SMB2_CLOSE then SMB2_CANCEL

Commit f580d27e8928 ("ksmbd: fix use-after-free of a deferred file_lock on
double SMB2_CANCEL") made smb2_cancel() skip a work whose state is
KSMBD_WORK_CANCELLED, so its cancel_fn cannot be fired a second time. But
KSMBD_WORK has three states (ACTIVE, CANCELLED, CLOSED), and the same
freeing producer path is reached for CLOSED too:

  SMB2_CLOSE on the locking handle -> set_close_state_blocked_works() sets
  the deferred work's state to KSMBD_WORK_CLOSED and wakes the smb2_lock()
  worker. The worker takes the non-ACTIVE early-exit, locks_free_lock()s
  the file_lock and, because the state is not KSMBD_WORK_CANCELLED, takes
  the STATUS_RANGE_NOT_LOCKED branch with "goto out2" -- which, like the
  cancelled branch, skips release_async_work(). The work stays on
  conn->async_requests with a live cancel_fn = smb2_remove_blocked_lock
  pointing at the freed file_lock.

A subsequent SMB2_CANCEL for the same AsyncId then passes the
KSMBD_WORK_CANCELLED-only guard (its state is KSMBD_WORK_CLOSED), so
smb2_cancel() fires cancel_fn again over the freed file_lock -- the same
use-after-free fixed, via SMB2_CLOSE instead of a first SMB2_CANCEL:

  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 (non-ACTIVE early-exit)
  ... cache file_lock_cache of size 192

Reproduced on mainline 7.1-rc7 (which already contains f580d27e8928) with
KASAN by an authenticated SMB client; the double-SMB2_CANCEL control is
silent on that kernel, so the splat is attributable to the CLOSE trigger.

Only an ACTIVE deferred work may have its cancel_fn fired: both terminal
states (CANCELLED and CLOSED) reach the smb2_lock() early-exit that frees
the file_lock and skips release_async_work(). Guard on KSMBD_WORK_ACTIVE
so any non-active work is skipped.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-64437?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64437?

Apply the vendor's patch.

## Is CVE-2026-64437 being exploited?

There is no known exploitation of CVE-2026-64437 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-2026-64437 and fix it if it is affected.

What it is: CVE-2026-64437 is a high-severity use after free vulnerability in Linux kernel, published on 25 Jul 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-2026-64437 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-2026-64437/ (Markdown: https://insights.sbomify.com/CVE-2026-64437/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64437
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64437
- OSV: https://osv.dev/vulnerability/CVE-2026-64437

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64437/
Summaries are generated and may contain mistakes; the official description above is the record.