# CVE-2026-93235: f2fs: fix to zero post-EOF data when extending file size

> Local attackers can read stale disk data beyond the file end after crash recovery due to improper zeroing in the f2fs filesystem.

- **Severity:** Not scored
- **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:** 24 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-93235, DEBIAN-CVE-2026-93235, GHSA-pxxc-gx8x-h7j2, UBUNTU-CVE-2026-93235

## What is CVE-2026-93235?

CVE-2026-93235 is a vulnerability in Linux, published on 24 Sep 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 to zero post-EOF data when extending file size

generic/794  4s ... - output mismatch (see /share/git/fstests/results//generic/794.out.bad)
    --- tests/generic/794.out   2026-06-12 08:46:32.766426241 +0800
    +++ /share/git/fstests/results//generic/794.out.bad 2026-07-05 18:32:55.000000000 +0800
    @@ -1,4 +1,16 @@
     QA output created by 794
     append_write
    +FAIL: non-zero data in gap [4080,4096) after shutdown+remount
    +000000 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a  >ZZZZZZZZZZZZZZZZ<
    +*
    +001000
     truncate_up
    ...
    (Run 'diff -u /share/git/fstests/tests/generic/794.out /share/git/fstests/results//generic/794.out.bad'  to see the entire diff)
Ran: generic/794
Failures: generic/794
Failed 1 of 1 tests

Steps of generic/794:
1. write 4096 bytes to file w/ 0x5a
2. use fiemap to get PBA of first block in file
3. truncate file to 4080
4. umount; write 4096 bytes to file w/ 0x5a directly via PBA; mount
5. extend filesize via
   a) append 4096 from offset 4096, or
   b) truncate 8192, or
   c) fallocate 4096 from offset 4096
6. verify the gap is zeroed in memory [4080,4096)
7. sync range 4096 from offset 4096; shutdown -f (flush meta before shutdown)
8. umount; mount; verify [4080,4096) is zeroed or not.

When extending file size (e.g. via truncate, fallocate, or write) across an
unaligned EOF boundary, we need to ensure that post-EOF data in the partial
page is zeroed out in pagecache and marked dirty, then writeback the cache to
persist zeroed data before committing inode w/ updated i_size.

This help to prevent stale disk data beyond the previous EOF from being exposed
after remounting or crash recovery.

Since f2fs is a LFS filesystem, we only support direct write via PBA in pinfile,
and pinfile has section-aligned filesize, so in Android, there should no problem,
but for other usage in different environment, let's fix this w/ fsync_mode=strict
mount option.

## Which versions are affected by CVE-2026-93235?


## How do I fix CVE-2026-93235?

Apply the vendor's patch.

## Is CVE-2026-93235 being exploited?

There is no known exploitation of CVE-2026-93235 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93235 and fix it if it is affected.

What it is: CVE-2026-93235 is a vulnerability in Linux, published on 24 Sep 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-2026-93235 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-2026-93235/ (Markdown: https://insights.sbomify.com/CVE-2026-93235/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93235
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93235
- OSV: https://osv.dev/vulnerability/CVE-2026-93235

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93235/
Summaries are generated and may contain mistakes; the official description above is the record.