# CVE-2026-89676: nfsd: fix stale s2s_cp_stateids IDR entry for async COPY

> A use-after-free vulnerability in the Linux kernel NFS server allows attackers to cause denial of service or execute arbitrary code via async COPY operations.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/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-100704, BELL-CVE-2026-89676, DEBIAN-CVE-2026-89676, GHSA-gwc7-hc26-hx5g, UBUNTU-CVE-2026-89676

## What is CVE-2026-89676?

CVE-2026-89676 is a critical 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 stale s2s_cp_stateids IDR entry for async COPY

For an async COPY, nfsd4_copy() called nfs4_init_copy_state() before
dup_copy_fields(), so the s2s_cp_stateids IDR was pointed at
&u->copy->cp_stateid -- memory in the per-rqstp COMPOUND buffer that is
reused by the next request. dup_copy_fields() copies only the value into
async_copy, so the IDR slot dangled at the transient buffer for the whole
background copy. Any IDR walker then dereferences reused request memory:
the laundromat reads cs_type from it and, if the bytes look like an
expired NFS4_COPYNOTIFY_STID, follows into
refcount_dec()/idr_remove()/kfree() on garbage; manage_cpntf_state() has
the same exposure via idr_find().

Duplicate the fields first, then register the stateid on the stable
async_copy. result->cb_stateid is unchanged.

## Which versions are affected by CVE-2026-89676?


## How do I fix CVE-2026-89676?

Apply the vendor's patch.

## Is CVE-2026-89676 being exploited?

There is no known exploitation of CVE-2026-89676 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89676 and fix it if it is affected.

What it is: CVE-2026-89676 is a critical 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-2026-89676 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-2026-89676/ (Markdown: https://insights.sbomify.com/CVE-2026-89676/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89676
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89676
- OSV: https://osv.dev/vulnerability/CVE-2026-89676

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89676/
Summaries are generated and may contain mistakes; the official description above is the record.