# CVE-2026-89644: btrfs: fix extent map leak in NOCOW direct I/O write

> A local attacker can trigger a memory leak in the Btrfs filesystem during direct I/O writes, potentially leading to resource exhaustion and denial of service.

- **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:** 11 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-100610, BELL-CVE-2026-89644, DEBIAN-CVE-2026-89644, GHSA-8844-3wf4-22v2, UBUNTU-CVE-2026-89644

## What is CVE-2026-89644?

CVE-2026-89644 is a memory corruption vulnerability in Linux, published on 11 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:

btrfs: fix extent map leak in NOCOW direct I/O write

btrfs_dio_iomap_begin() calls btrfs_get_extent(), which returns an
extent map reference that must be dropped on all exit paths.

For direct writes into a NOCOW range, btrfs_get_blocks_direct_write()
keeps using that extent map and asks btrfs_create_dio_extent() to
allocate the ordered extent. If that fails, for example because
btrfs_alloc_ordered_extent() fails, the function returns the error
without dropping the input extent map. The PREALLOC path avoided this by
dropping the input extent map before replacing it with the newly created
one.

Check the error from btrfs_create_dio_extent() before replacing the
map and drop the input extent map on failure.

## Which versions are affected by CVE-2026-89644?


## How do I fix CVE-2026-89644?

Apply the vendor's patch.

## Is CVE-2026-89644 being exploited?

There is no known exploitation of CVE-2026-89644 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89644 and fix it if it is affected.

What it is: CVE-2026-89644 is a memory corruption vulnerability in Linux, published on 11 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-2026-89644 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-2026-89644/ (Markdown: https://insights.sbomify.com/CVE-2026-89644/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89644
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89644
- OSV: https://osv.dev/vulnerability/CVE-2026-89644

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89644/
Summaries are generated and may contain mistakes; the official description above is the record.