# CVE-2025-38691: pNFS: Fix uninited ptr deref in block/scsi layout

> A null pointer dereference in the Linux kernel pNFS block/scsi layout allows attackers to cause a denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** 4 Sep 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-66800, AZL-73920, BELL-CVE-2025-38691, DEBIAN-CVE-2025-38691, GHSA-94hx-q75x-2q84, ROOT-OS-DEBIAN-11-CVE-2025-38691, ROOT-OS-DEBIAN-12-CVE-2025-38691, ROOT-OS-UBUNTU-2204-CVE-2025-38691, ROOT-OS-UBUNTU-2404-CVE-2025-38691, UBUNTU-CVE-2025-38691

## What is CVE-2025-38691?

CVE-2025-38691 is a medium-severity vulnerability in Debian Debian Linux, published on 4 Sep 2025. 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:

pNFS: Fix uninited ptr deref in block/scsi layout

The error occurs on the third attempt to encode extents. When function
ext_tree_prepare_commit() reallocates a larger buffer to retry encoding
extents, the "layoutupdate_pages" page array is initialized only after the
retry loop. But ext_tree_free_commitdata() is called on every iteration
and tries to put pages in the array, thus dereferencing uninitialized
pointers.

An additional problem is that there is no limit on the maximum possible
buffer_size. When there are too many extents, the client may create a
layoutcommit that is larger than the maximum possible RPC size accepted
by the server.

During testing, we observed two typical scenarios. First, one memory page
for extents is enough when we work with small files, append data to the
end of the file, or preallocate extents before writing. But when we fill
a new large file without preallocating, the number of extents can be huge,
and counting the number of written extents in ext_tree_encode_commit()
does not help much. Since this number increases even more between
unlocking and locking of ext_tree, the reallocated buffer may not be
large enough again and again.

Weakness: CWE-908 (Use of Uninitialized Resource)

## Which versions are affected by CVE-2025-38691?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-38691?

Apply the vendor's patch.

## Is CVE-2025-38691 being exploited?

There is no known exploitation of CVE-2025-38691 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-2025-38691 and fix it if it is affected.

What it is: CVE-2025-38691 is a medium-severity vulnerability in Debian Debian Linux, published on 4 Sep 2025. 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-2025-38691 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-2025-38691/ (Markdown: https://insights.sbomify.com/CVE-2025-38691/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38691
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38691
- OSV: https://osv.dev/vulnerability/CVE-2025-38691

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38691/
Summaries are generated and may contain mistakes; the official description above is the record.