# CVE-2026-89706: nfsd: Reset write verifier when async COPY writeback fails


- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100868, BELL-CVE-2026-89706, DEBIAN-CVE-2026-89706, GHSA-gfmq-vxg4-w276, UBUNTU-CVE-2026-89706

## What is CVE-2026-89706?

CVE-2026-89706 is a high-severity vulnerability in Linux, published on 11 Sep 2026. 

### Official description

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

nfsd: Reset write verifier when async COPY writeback fails

Async COPY captures nn->writeverf at request time and reports it to
the client via CB_OFFLOAD after the worker kthread completes. When
the post-copy vfs_fsync_range() or filemap_check_wb_err() in
_nfsd_copy_file_range() reports an error, the worker correctly
leaves NFSD4_COPY_F_COMMITTED clear so that CB_OFFLOAD encodes
wr_stable_how as NFS_UNSTABLE, but the server's write verifier is
not rotated.

A client that receives NFS_UNSTABLE in CB_OFFLOAD follows up with
COMMIT to make the copied data durable. With the verifier
unchanged, COMMIT returns the same value the client just received
via CB_OFFLOAD, and the client concludes the copy is durable --
silently dropping the data whose writeback in fact failed. This
violates the UNSTABLE+COMMIT durability contract (RFC 7862 section
15.1, RFC 8881 section 18.32) and matches the bug just fixed in
nfsd_vfs_write() and nfsd_commit().

Rotate nn->writeverf at the writeback-failure site. The async COPY
worker has no svc_rqst, so commit_reset_write_verifier() is not
available here; calling nfsd_reset_write_verifier() directly
mirrors the trace-less reset already used by
nfsd_file_check_write_error() for the same purpose. Filter out
-EAGAIN and -ESTALE, matching commit_reset_write_verifier(), since
neither indicates a durable-storage failure.

## Which versions are affected by CVE-2026-89706?


## How do I fix CVE-2026-89706?

Upgrade to a fixed version.

## Is CVE-2026-89706 being exploited?

There is no known exploitation of CVE-2026-89706 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89706 and fix it if it is affected.

What it is: CVE-2026-89706 is a high-severity vulnerability in Linux, published on 11 Sep 2026. 
Exploitation: There is no known exploitation of CVE-2026-89706 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-2026-89706/ (Markdown: https://insights.sbomify.com/CVE-2026-89706/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89706
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89706
- OSV: https://osv.dev/vulnerability/CVE-2026-89706

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89706/
Summaries are generated and may contain mistakes; the official description above is the record.