# 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.

- **Severity:** Not scored
- **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:** 17 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-102578, BELL-CVE-2026-90155, DEBIAN-CVE-2026-90155, GHSA-52g3-8w7f-v5w2, UBUNTU-CVE-2026-90155

## 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.

## Is CVE-2026-90155 being exploited?

There is no known exploitation of CVE-2026-90155 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90155 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-90155 in the wild and no public exploit code.

Affected product: Linux. 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-2026-90155/ (Markdown: https://insights.sbomify.com/CVE-2026-90155/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90155
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90155
- OSV: https://osv.dev/vulnerability/CVE-2026-90155

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90155/
Summaries are generated and may contain mistakes; the official description above is the record.