# CVE-2025-37858: fs/jfs: Prevent integer overflow in AG size calculation

> An integer overflow in the Linux kernel JFS filesystem allows attackers to cause crashes or potential code execution via malformed on-disk structures.

- **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:** 9 May 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-37858, DEBIAN-CVE-2025-37858, GHSA-886x-q2xh-8p43, ROOT-OS-DEBIAN-12-CVE-2025-37858, ROOT-OS-UBUNTU-2204-CVE-2025-37858, ROOT-OS-UBUNTU-2404-CVE-2025-37858, UBUNTU-CVE-2025-37858

## What is CVE-2025-37858?

CVE-2025-37858 is a medium-severity vulnerability in Debian Debian Linux, published on 9 May 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:

fs/jfs: Prevent integer overflow in AG size calculation

The JFS filesystem calculates allocation group (AG) size using 1 <<
l2agsize in dbExtendFS(). When l2agsize exceeds 31 (possible with >2TB
aggregates on 32-bit systems), this 32-bit shift operation causes undefined
behavior and improper AG sizing.

On 32-bit architectures:
- Left-shifting 1 by 32+ bits results in 0 due to integer overflow
- This creates invalid AG sizes (0 or garbage values) in
sbi->bmap->db_agsize
- Subsequent block allocations would reference invalid AG structures
- Could lead to:
  - Filesystem corruption during extend operations
  - Kernel crashes due to invalid memory accesses
  - Security vulnerabilities via malformed on-disk structures

Fix by casting to s64 before shifting:
bmp->db_agsize = (s64)1 << l2agsize;

This ensures 64-bit arithmetic even on 32-bit architectures. The cast
matches the data type of db_agsize (s64) and follows similar patterns in
JFS block calculation code.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2025-37858?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-37858?

Apply the vendor's patch.

## Is CVE-2025-37858 being exploited?

There is no known exploitation of CVE-2025-37858 in the wild and no public exploit code.

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- [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-2025-37858 and fix it if it is affected.

What it is: CVE-2025-37858 is a medium-severity vulnerability in Debian Debian Linux, published on 9 May 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-2025-37858 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-2025-37858/ (Markdown: https://insights.sbomify.com/CVE-2025-37858/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-37858
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-37858
- OSV: https://osv.dev/vulnerability/CVE-2025-37858

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-37858/
Summaries are generated and may contain mistakes; the official description above is the record.