# CVE-2026-89682: nfsd: fix fcache_disposal UAF by inlining dispose state into nfsd_net

> A use-after-free in the Linux kernel NFS server allows attackers to cause denial of service or execute arbitrary code via race conditions during network namespace teardown.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-100803, BELL-CVE-2026-89682, DEBIAN-CVE-2026-89682, GHSA-hvfh-9745-ghhq, UBUNTU-CVE-2026-89682

## What is CVE-2026-89682?

CVE-2026-89682 is a high-severity use after free vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

nfsd: fix fcache_disposal UAF by inlining dispose state into nfsd_net

nfsd_file_dispose_list_delayed() defers fput() to nfsd service threads
via a per-net freeme queue, preventing the shrinker and GC worker from
bearing the cost of closing files (see ffb402596147).  However, the
queue lives in a separately-allocated struct nfsd_fcache_disposal that
is freed by nfsd_free_fcache_disposal_net() during per-net teardown.
The global shrinker, laundrette, and fsnotify callbacks can still be
inside nfsd_file_dispose_list_delayed() dereferencing that pointer,
causing a use-after-free.

Inline the spinlock and freeme list directly into struct nfsd_net (as
fcache_dispose_lock and fcache_dispose_list), eliminating the separately
allocated struct nfsd_fcache_disposal entirely.  These fields now have
the same lifetime as the net namespace itself, so there is no dangling
pointer to chase.

nfsd_file_cache_start_net() now just initializes the inline fields and
cannot fail due to allocation.  nfsd_file_cache_shutdown_net() drains
the inline list directly instead of freeing a separate struct.  The
alloc/free helpers are removed.

## Which versions are affected by CVE-2026-89682?


## How do I fix CVE-2026-89682?

Apply the vendor's patch.

## Is CVE-2026-89682 being exploited?

There is no known exploitation of CVE-2026-89682 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89682 and fix it if it is affected.

What it is: CVE-2026-89682 is a high-severity use after free vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89682 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-2026-89682/ (Markdown: https://insights.sbomify.com/CVE-2026-89682/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89682
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89682
- OSV: https://osv.dev/vulnerability/CVE-2026-89682

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89682/
Summaries are generated and may contain mistakes; the official description above is the record.