# CVE-2026-80807: nilfs2: reject invalid block index in GC ioctl

> A local attacker can trigger a denial of service in the Linux kernel nilfs2 filesystem by exploiting an integer overflow in the GC ioctl.

- **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:** 4 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-99510, BELL-CVE-2026-80807, DEBIAN-CVE-2026-80807, GHSA-h6ww-mgj9-p3pf, UBUNTU-CVE-2026-80807

## What is CVE-2026-80807?

CVE-2026-80807 is a vulnerability in Linux, published on 4 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:

nilfs2: reject invalid block index in GC ioctl

Syzbot reported list corruption caused by a double list_add_tail() call on
bh->b_assoc_buffers within nilfs_lookup_dirty_data_buffers().

Analysis revealed that the root cause was the insertion of a page/folio
with a page index of ULONG_MAX into the page cache via the GC ioctl.
filemap_get_folios_tag(), called by nilfs_lookup_dirty_data_buffers(),
repeatedly detects a dirty folio with a page index of ULONG_MAX due to
index wrap-around, leading to duplicate processing of dirty buffers.

As a preparatory step, the GC ioctl loads the page/folio of the block to
be moved during GC and inserts it into the page cache based on information
in the nilfs_vdesc structure passed as an argument.  Normally, this does
not cause issues because the user-space GC library configures the
nilfs_vdesc structure properly.  However, since there is no range check on
the parameters determining the page index, a request with artificially
crafted parameters -- such as those generated by Syzbot -- can result in a
page/folio being inserted with a page index of ULONG_MAX, triggering the
above problem.

This resolves the issue by checking the ranges of 'vd_offset' and
'vd_vblocknr' in the nilfs_vdesc structure that determine the page index,
thereby preventing the invalid page/folio insertions.

## Which versions are affected by CVE-2026-80807?


## How do I fix CVE-2026-80807?

Apply the vendor's patch.

## Is CVE-2026-80807 being exploited?

There is no known exploitation of CVE-2026-80807 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80807 and fix it if it is affected.

What it is: CVE-2026-80807 is a vulnerability in Linux, published on 4 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-2026-80807 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-2026-80807/ (Markdown: https://insights.sbomify.com/CVE-2026-80807/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80807
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80807
- OSV: https://osv.dev/vulnerability/CVE-2026-80807

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80807/
Summaries are generated and may contain mistakes; the official description above is the record.