# CVE-2025-38527: smb: client: fix use-after-free in cifs_oplock_break

> A race condition in the Linux kernel SMB client allows a use-after-free during unmount, potentially leading to code execution or denial of service.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 16 Aug 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-66401, AZL-73554, BELL-CVE-2025-38527, DEBIAN-CVE-2025-38527, GHSA-hm6q-hprh-4f22, ROOT-OS-DEBIAN-11-CVE-2025-38527, ROOT-OS-DEBIAN-12-CVE-2025-38527, ROOT-OS-DEBIAN-13-CVE-2025-38527, ROOT-OS-UBUNTU-2204-CVE-2025-38527, ROOT-OS-UBUNTU-2404-CVE-2025-38527, UBUNTU-CVE-2025-38527

## What is CVE-2025-38527?

CVE-2025-38527 is a critical use after free vulnerability in Debian Debian Linux, published on 16 Aug 2025. 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: fix use-after-free in cifs_oplock_break

A race condition can occur in cifs_oplock_break() leading to a
use-after-free of the cinode structure when unmounting:

  cifs_oplock_break()
    _cifsFileInfo_put(cfile)
      cifsFileInfo_put_final()
        cifs_sb_deactive()
          [last ref, start releasing sb]
            kill_sb()
              kill_anon_super()
                generic_shutdown_super()
                  evict_inodes()
                    dispose_list()
                      evict()
                        destroy_inode()
                          call_rcu(&inode->i_rcu, i_callback)
    spin_lock(&cinode->open_file_lock)  <- OK
                            [later] i_callback()
                              cifs_free_inode()
                                kmem_cache_free(cinode)
    spin_unlock(&cinode->open_file_lock)  <- UAF
    cifs_done_oplock_break(cinode)       <- UAF

The issue occurs when umount has already released its reference to the
superblock. When _cifsFileInfo_put() calls cifs_sb_deactive(), this
releases the last reference, triggering the immediate cleanup of all
inodes under RCU. However, cifs_oplock_break() continues to access the
cinode after this point, resulting in use-after-free.

Fix this by holding an extra reference to the superblock during the
entire oplock break operation. This ensures that the superblock and
its inodes remain valid until the oplock break completes.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2025-38527?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-38527?

Apply the vendor's patch.

## Is CVE-2025-38527 being exploited?

There is no known exploitation of CVE-2025-38527 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-38527 and fix it if it is affected.

What it is: CVE-2025-38527 is a critical use after free vulnerability in Debian Debian Linux, published on 16 Aug 2025. 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-2025-38527 in the wild and no public exploit code.

Affected product: Debian Debian 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-2025-38527/ (Markdown: https://insights.sbomify.com/CVE-2025-38527/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38527
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38527
- OSV: https://osv.dev/vulnerability/CVE-2025-38527

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38527/
Summaries are generated and may contain mistakes; the official description above is the record.