# CVE-2025-38709: loop: Avoid updating block size under exclusive owner

> A race condition in the Linux kernel loop device allows block size changes during mount, causing filesystem confusion and potential 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:** 11 May 2026
- **Also known as:** AZL-66812, AZL-71257, BELL-CVE-2025-38709, DEBIAN-CVE-2025-38709, GHSA-4rvm-hh4p-2jfj, ROOT-OS-DEBIAN-11-CVE-2025-38709, ROOT-OS-DEBIAN-12-CVE-2025-38709, ROOT-OS-UBUNTU-2204-CVE-2025-38709, ROOT-OS-UBUNTU-2404-CVE-2025-38709, UBUNTU-CVE-2025-38709

## What is CVE-2025-38709?

CVE-2025-38709 is a medium-severity vulnerability in Linux kernel, 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:

loop: Avoid updating block size under exclusive owner

Syzbot came up with a reproducer where a loop device block size is
changed underneath a mounted filesystem. This causes a mismatch between
the block device block size and the block size stored in the superblock
causing confusion in various places such as fs/buffer.c. The particular
issue triggered by syzbot was a warning in __getblk_slow() due to
requested buffer size not matching block device block size.

Fix the problem by getting exclusive hold of the loop device to change
its block size. This fails if somebody (such as filesystem) has already
an exclusive ownership of the block device and thus prevents modifying
the loop device under some exclusive owner which doesn't expect it.

## Which versions are affected by CVE-2025-38709?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-38709?

Apply the vendor's patch.

## Is CVE-2025-38709 being exploited?

There is no known exploitation of CVE-2025-38709 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-38709 and fix it if it is affected.

What it is: CVE-2025-38709 is a medium-severity vulnerability in Linux kernel, 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-2025-38709 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2025-38709/ (Markdown: https://insights.sbomify.com/CVE-2025-38709/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38709
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38709
- OSV: https://osv.dev/vulnerability/CVE-2025-38709

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38709/
Summaries are generated and may contain mistakes; the official description above is the record.