# CVE-2026-97556: smb: client: avoid leaking refcount when cifs_sb_tlink() fails

> A refcount leak in the Linux kernel CIFS client causes a crash during unmount when multiuser mode is enabled, leading to denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-104327, BELL-CVE-2026-97556, DEBIAN-CVE-2026-97556, GHSA-v7vw-58j3-xcmw, UBUNTU-CVE-2026-97556

## What is CVE-2026-97556?

CVE-2026-97556 is a denial of service vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

smb: client: avoid leaking refcount when cifs_sb_tlink() fails

cifs_oplock_break() takes over the reference that
cifs_queue_oplock_break() acquired when it queued the work, and drops it
with _cifsFileInfo_put() once the break has been processed.

Only in setups with "-o multiuser", cifs_sb_tlink() may fail, at which
point cifs_oplock_break() returns without putting the file reference,
mirroring the reference leak we already fixed in the companion patch to
cifs_queue_oplock_break().

This would trigger a crash due to busy inodes on the next unmount:

  BUG: Dentry ... still in use (1) [unmount of cifs cifs]
  VFS: Busy inodes after unmount of cifs (cifs)

Drop the reference on that path as well. Doing so before the out label
mirrors the normal path, which also puts the reference before
cifs_done_oplock_break().

Found by Sashiko code review. The failure path was not exercised at
runtime.

## Which versions are affected by CVE-2026-97556?


## How do I fix CVE-2026-97556?

Apply the vendor's patch.

## Is CVE-2026-97556 being exploited?

There is no known exploitation of CVE-2026-97556 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97556 and fix it if it is affected.

What it is: CVE-2026-97556 is a denial of service vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-97556 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-2026-97556/ (Markdown: https://insights.sbomify.com/CVE-2026-97556/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97556
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97556
- OSV: https://osv.dev/vulnerability/CVE-2026-97556

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97556/
Summaries are generated and may contain mistakes; the official description above is the record.