# CVE-2025-40198: ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()

> A buffer over-read in the Linux kernel ext4 filesystem allows attackers to cause denial of service or disclose sensitive memory information.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 12 Nov 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-70067, BELL-CVE-2025-40198, DEBIAN-CVE-2025-40198, GHSA-w7vv-57v2-cqgf, ROOT-OS-DEBIAN-11-CVE-2025-40198, ROOT-OS-UBUNTU-2204-CVE-2025-40198, ROOT-OS-UBUNTU-2404-CVE-2025-40198, UBUNTU-CVE-2025-40198

## What is CVE-2025-40198?

CVE-2025-40198 is a high-severity memory corruption vulnerability in Linux, published on 12 Nov 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()

Unlike other strings in the ext4 superblock, we rely on tune2fs to
make sure s_mount_opts is NUL terminated.  Harden
parse_apply_sb_mount_options() by treating s_mount_opts as a potential
__nonstring.

## Which versions are affected by CVE-2025-40198?


## How do I fix CVE-2025-40198?

Apply the vendor's patch.

## Is CVE-2025-40198 being exploited?

There is no known exploitation of CVE-2025-40198 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40198 and fix it if it is affected.

What it is: CVE-2025-40198 is a high-severity memory corruption vulnerability in Linux, published on 12 Nov 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2025-40198 in the wild and no public exploit code.

Affected product: 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-2025-40198/ (Markdown: https://insights.sbomify.com/CVE-2025-40198/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40198
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40198
- OSV: https://osv.dev/vulnerability/CVE-2025-40198

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40198/
Summaries are generated and may contain mistakes; the official description above is the record.