# CVE-2026-89546: SUNRPC: close backchannel before destroying callback service

> A race condition in the Linux kernel SUNRPC subsystem can lead to memory leaks or use-after-free errors during NFS callback service teardown, potentially causing a denial of service.

- **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:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-89546, GHSA-ggx6-mw65-hcjr, UBUNTU-CVE-2026-89546

## What is CVE-2026-89546?

CVE-2026-89546 is a critical 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:

SUNRPC: close backchannel before destroying callback service

A backchannel receive can complete a request while the NFS callback
service is being torn down.  xprt_complete_bc_request() removes the
request from bc_pa_list, drops bc_alloc_count, marks the request in use,
and then asks xprt_enqueue_bc_request() to hand it to the callback
service.

If teardown has already cleared xprt->bc_serv, xprt_enqueue_bc_request()
currently returns without enqueueing or freeing the committed request.
The xprt_get() taken on entry is leaked as well.  If the producer wins
the race before bc_serv is cleared, it can also enqueue onto sv_cb_list
after nfs_callback_down() has stopped the callback threads, leaving the
request linked to a svc_serv that is about to be freed.

Close the producer side before callback threads are stopped.  Add
xprt_svc_shutdown_bc() to clear xprt->bc_serv under bc_pa_lock, and call
it on callback shutdown and callback-start failure before stopping the
service threads.  Requests that lose the NULL transition in
xprt_enqueue_bc_request() are released through the normal backchannel
free path after balancing bc_slot_count.  Finally, drain any remaining
sv_cb_list requests after the callback threads have stopped and before
svc_destroy() frees the service.

## Which versions are affected by CVE-2026-89546?


## How do I fix CVE-2026-89546?

Apply the vendor's patch.

## Is CVE-2026-89546 being exploited?

There is no known exploitation of CVE-2026-89546 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89546 and fix it if it is affected.

What it is: CVE-2026-89546 is a critical 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-2026-89546 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-2026-89546/ (Markdown: https://insights.sbomify.com/CVE-2026-89546/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89546
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89546
- OSV: https://osv.dev/vulnerability/CVE-2026-89546

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89546/
Summaries are generated and may contain mistakes; the official description above is the record.