# CVE-2025-21736: nilfs2: fix possible int overflows in nilfs_fiemap()

> An integer overflow in the nilfs2 filesystem's fiemap function could lead to a denial of service, requiring a kernel patch.

- **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:** 27 Feb 2025
- **Updated:** 11 May 2026
- **Also known as:** AZL-57832, BELL-CVE-2025-21736, DEBIAN-CVE-2025-21736, GHSA-jj6f-649q-27mh, ROOT-OS-UBUNTU-2404-CVE-2025-21736, UBUNTU-CVE-2025-21736

## What is CVE-2025-21736?

CVE-2025-21736 is a medium-severity vulnerability in Linux kernel, published on 27 Feb 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:

nilfs2: fix possible int overflows in nilfs_fiemap()

Since nilfs_bmap_lookup_contig() in nilfs_fiemap() calculates its result
by being prepared to go through potentially maxblocks == INT_MAX blocks,
the value in n may experience an overflow caused by left shift of blkbits.

While it is extremely unlikely to occur, play it safe and cast right hand
expression to wider type to mitigate the issue.

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

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2025-21736?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21736?

Apply the vendor's patch.

## Is CVE-2025-21736 being exploited?

There is no known exploitation of CVE-2025-21736 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-2025-21736 and fix it if it is affected.

What it is: CVE-2025-21736 is a medium-severity vulnerability in Linux kernel, published on 27 Feb 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-2025-21736 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-2025-21736/ (Markdown: https://insights.sbomify.com/CVE-2025-21736/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21736
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21736
- OSV: https://osv.dev/vulnerability/CVE-2025-21736

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21736/
Summaries are generated and may contain mistakes; the official description above is the record.