# CVE-2025-40233: ocfs2: clear extent cache after moving/defragmenting extents

> A stale extent cache in the Linux kernel OCFS2 filesystem can trigger a BUG_ON crash during specific file operations, causing a denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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 Dec 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-40233, DEBIAN-CVE-2025-40233, GHSA-pmpf-32ww-gfmp, ROOT-OS-DEBIAN-11-CVE-2025-40233, ROOT-OS-UBUNTU-2404-CVE-2025-40233, UBUNTU-CVE-2025-40233

## What is CVE-2025-40233?

CVE-2025-40233 is a high-severity denial of service vulnerability in Linux, published on 4 Dec 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:

ocfs2: clear extent cache after moving/defragmenting extents

The extent map cache can become stale when extents are moved or
defragmented, causing subsequent operations to see outdated extent flags. 
This triggers a BUG_ON in ocfs2_refcount_cal_cow_clusters().

The problem occurs when:
1. copy_file_range() creates a reflinked extent with OCFS2_EXT_REFCOUNTED
2. ioctl(FITRIM) triggers ocfs2_move_extents()
3. __ocfs2_move_extents_range() reads and caches the extent (flags=0x2)
4. ocfs2_move_extent()/ocfs2_defrag_extent() calls __ocfs2_move_extent()
   which clears OCFS2_EXT_REFCOUNTED flag on disk (flags=0x0)
5. The extent map cache is not invalidated after the move
6. Later write() operations read stale cached flags (0x2) but disk has
   updated flags (0x0), causing a mismatch
7. BUG_ON(!(rec->e_flags & OCFS2_EXT_REFCOUNTED)) triggers

Fix by clearing the extent map cache after each extent move/defrag
operation in __ocfs2_move_extents_range().  This ensures subsequent
operations read fresh extent data from disk.

## Which versions are affected by CVE-2025-40233?


## How do I fix CVE-2025-40233?

Apply the vendor's patch.

## Is CVE-2025-40233 being exploited?

There is no known exploitation of CVE-2025-40233 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40233 and fix it if it is affected.

What it is: CVE-2025-40233 is a high-severity denial of service vulnerability in Linux, published on 4 Dec 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-2025-40233 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-2025-40233/ (Markdown: https://insights.sbomify.com/CVE-2025-40233/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40233
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40233
- OSV: https://osv.dev/vulnerability/CVE-2025-40233

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40233/
Summaries are generated and may contain mistakes; the official description above is the record.