# CVE-2026-89540: sunrpc: init gssp_lock before publishing proc entry

> A race condition in the Linux kernel sunrpc module allows concurrent access to an uninitialized mutex, potentially causing crashes or memory leaks.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** 19 Oct 2026
- **Also known as:** AZL-100787, BELL-CVE-2026-89540, DEBIAN-CVE-2026-89540, GHSA-gwh2-5395-p8p6, UBUNTU-CVE-2026-89540

## What is CVE-2026-89540?

CVE-2026-89540 is a high-severity 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:

sunrpc: init gssp_lock before publishing proc entry

create_use_gss_proxy_proc_entry() publishes /proc/net/rpc/use-gss-proxy
via proc_create_data() before init_gssp_clnt() runs mutex_init() on
sn->gssp_lock.  Once the dentry is linked under proc_subdir_lock it is
immediately reachable from userspace, so a write that lands in the
window drives set_gssp_clnt() into mutex_lock() on a zero-initialized
struct mutex.

    create_use_gss_proxy_proc_entry(net)
      proc_create_data("use-gss-proxy", ...)   /* dentry live */
      init_gssp_clnt(sn)
        mutex_init(&sn->gssp_lock)             /* too late */

    write_gssp()
      set_gssp_clnt(net)
        mutex_lock(&sn->gssp_lock)             /* uninitialized */
        gssp_rpc_create(...)
        sn->gssp_clnt = clnt
        mutex_unlock(&sn->gssp_lock)

The window spans only the two statements between proc_create_data()
returning and init_gssp_clnt(), so a writer reaches it only if the
registering thread is preempted there while another task is already
opening the freshly published file.  register_pernet_subsys() runs in
preemptible context under pernet_ops_rwsem, so that preemption is
possible, and the window widens on auth_rpcgss module load, when the
proc entry is created for every live net namespace whose tasks are
already running.  A writer that wins the race locks a zero-filled
struct mutex.  On CONFIG_DEBUG_MUTEXES the missing magic value trips a
"lock used without init" splat; on a production kernel the fast path
acquires the lock via CMPXCHG(owner, 0, current).  In the latter case
a second writer that arrives before init_gssp_clnt() re-zeroes owner
can enter set_gssp_clnt() concurrently, shut down the first writer's
clnt while it is still in use, and leak the loser's clnt.

Fix by initializing sn->gssp_lock in sunrpc_init_net() so its lifetime
matches the sunrpc_net it lives in.  sn->gssp_clnt is already NULL from
the kzalloc that backs net_generic storage, so the lazy helper is no
longer needed; drop init_gssp_clnt(), its prototype, and the call from
create_use_gss_proxy_proc_entry().  sunrpc.ko is a build-time
dependency of auth_rpcgss.ko, so sunrpc_init_net() has always run on
every netns before any auth_gss pernet init can publish the proc
entry.

## Which versions are affected by CVE-2026-89540?


## How do I fix CVE-2026-89540?

Apply the vendor's patch.

## Is CVE-2026-89540 being exploited?

There is no known exploitation of CVE-2026-89540 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89540 and fix it if it is affected.

What it is: CVE-2026-89540 is a high-severity 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-2026-89540 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-2026-89540/ (Markdown: https://insights.sbomify.com/CVE-2026-89540/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89540
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89540
- OSV: https://osv.dev/vulnerability/CVE-2026-89540

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89540/
Summaries are generated and may contain mistakes; the official description above is the record.