# CVE-2026-63812: f2fs: fix incorrect FI_NO_EXTENT handling in __destroy_extent_node()

> Incorrect handling of extent node destruction in the f2fs filesystem can lead to stale cached data and filesystem corruption errors.

- **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:** 19 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-63812, DEBIAN-CVE-2026-63812, GHSA-7w3g-6v3x-44mp, UBUNTU-CVE-2026-63812

## What is CVE-2026-63812?

CVE-2026-63812 is a high-severity vulnerability in Linux, published on 19 Jul 2026. 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:

f2fs: fix incorrect FI_NO_EXTENT handling in __destroy_extent_node()

When __destroy_extent_node() sets the inode flag FI_NO_EXTENT, it does
not reset the length of the largest extent to 0 and update the inode
folio. Since modifications to the extent tree are disallowed afterward,
the cached largest extent may become stale. This can trigger the
following error in xfstests generic/388:

F2FS-fs (dm-0): sanity_check_extent_cache: inode (ino=1761) extent info [220057, 57, 6] is incorrect, run fsck to fix

In the f2fs_drop_inode path, __destroy_extent_node() does not need to
guarantee that et->node_cnt is 0, because concurrency with writeback
is expected in this path, and writeback may update the extent cache.

This patch reverts commit ed78aeebef05 ("f2fs: fix node_cnt race between
extent node destroy and writeback"), and remove the unnecessary zero
check of et->node_cnt.

## Which versions are affected by CVE-2026-63812?


## How do I fix CVE-2026-63812?

Apply the vendor's patch.

## Is CVE-2026-63812 being exploited?

There is no known exploitation of CVE-2026-63812 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63812 and fix it if it is affected.

What it is: CVE-2026-63812 is a high-severity vulnerability in Linux, published on 19 Jul 2026. 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-2026-63812 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-2026-63812/ (Markdown: https://insights.sbomify.com/CVE-2026-63812/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63812
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63812
- OSV: https://osv.dev/vulnerability/CVE-2026-63812

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63812/
Summaries are generated and may contain mistakes; the official description above is the record.