# CVE-2026-90418: nilfs2: fix BUG in nilfs_copy_dirty_pages() on dirty state mismatch

> A local attacker can trigger a kernel BUG in the nilfs2 filesystem by exploiting a dirty state mismatch, causing a system crash.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102522, BELL-CVE-2026-90418, DEBIAN-CVE-2026-90418, GHSA-c854-fhx8-wg6w, UBUNTU-CVE-2026-90418

## What is CVE-2026-90418?

CVE-2026-90418 is a denial of service vulnerability in Linux, published on 17 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: fix BUG in nilfs_copy_dirty_pages() on dirty state mismatch

Syzbot reported a kernel BUG triggered within nilfs_copy_dirty_pages(),
which copies dirty DAT file folios/pages to its shadow page cache.  The
BUG occurs when a retrieved dirty folio/page unexpectedly loses its
'dirty' status.

This issue arises because, since the commit referenced below, the 'dirty'
flag of a folio/page can be cleared asynchronously after the filesystem
detects metadata corruption and transitions to read-only mode.

Resolve the issue by returning an -EROFS error if the filesystem has
transitioned to read-only mode.  Also change the behavior to issue a
kernel warning only once instead of triggering a kernel BUG when this
unexpected 'dirty' state is detected while the filesystem is not in
read-only mode.

## Which versions are affected by CVE-2026-90418?


## How do I fix CVE-2026-90418?

Apply the vendor's patch.

## Is CVE-2026-90418 being exploited?

There is no known exploitation of CVE-2026-90418 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90418 and fix it if it is affected.

What it is: CVE-2026-90418 is a denial of service vulnerability in Linux, published on 17 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-2026-90418 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-2026-90418/ (Markdown: https://insights.sbomify.com/CVE-2026-90418/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90418
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90418
- OSV: https://osv.dev/vulnerability/CVE-2026-90418

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90418/
Summaries are generated and may contain mistakes; the official description above is the record.