# CVE-2026-97557: smb: client: avoid leaking refcount in cifs_queue_oplock_break()

> A refcount leak in the Linux kernel CIFS client causes kernel panics during unmount, leading to denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-104543, BELL-CVE-2026-97557, DEBIAN-CVE-2026-97557, GHSA-v47h-9mpw-4682, UBUNTU-CVE-2026-97557

## What is CVE-2026-97557?

CVE-2026-97557 is a high-severity denial of service vulnerability in Linux, published on 25 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

smb: client: avoid leaking refcount in cifs_queue_oplock_break()

cifs_queue_oplock_break() unconditionally takes a reference on the
target file before queueing cifs_oplock_break(). Only that work item
decreases the reference counter again.

If another oplock break arrives while that work is still queued,
queue_work() will return false and not queue this second work item. As a
result, we will never reach the point to drop the file reference again
and are leaking this reference. This can be triggered when interacting
with a slow-responding server.

As a result, later unmount operations for this file system will fail with

  BUG: Dentry ... still in use (1) [unmount of cifs cifs]
  VFS: Busy inodes after unmount of cifs (cifs)
  kernel BUG at fs/super.c:777!

Fix this by only incrementing the reference count if the work has been
queued successfully. Taking it after queue_work() is safe because all
three callers hold tcon->open_file_lock across the call and
_cifsFileInfo_put() decrements under that same lock, so a worker that
starts the handler in the window cannot drop the reference before it has
been taken.

## Which versions are affected by CVE-2026-97557?


## How do I fix CVE-2026-97557?

Apply the vendor's patch.

## Is CVE-2026-97557 being exploited?

There is no known exploitation of CVE-2026-97557 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97557 and fix it if it is affected.

What it is: CVE-2026-97557 is a high-severity denial of service vulnerability in Linux, published on 25 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-97557 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-2026-97557/ (Markdown: https://insights.sbomify.com/CVE-2026-97557/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97557
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97557
- OSV: https://osv.dev/vulnerability/CVE-2026-97557

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97557/
Summaries are generated and may contain mistakes; the official description above is the record.