CVE-2026-89658 NFSD: Prevent client use-after-free during NFSv4.0 revoked-state cleanup
A use-after-free in the Linux kernel NFSD allows attackers to cause denial of service or execute code via race conditions during NFSv4.0 state cleanup.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89658?
CVE-2026-89658 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: Prevent client use-after-free during NFSv4.0 revoked-state cleanup
nfs40_clean_admin_revoked() takes a stateid reference under clp->cl_lock, drops nn->client_lock, and calls nfsd4_drop_revoked_stid(), which dereferences the stateid's client through s->sc_client->cl_lock. The stateid reference does not pin the client, so a teardown racing the dropped lock can free the client while nfsd4_drop_revoked_stid() is still using it.
This cleanup runs from the laundromat, so a periodic sweep can race force_expire_client() driven by a write to the clients/<id>/ctl file.
Skip a client that is already expiring and otherwise pin it with cl_rpc_users under client_lock before dropping the lock, matching nfsd4_revoke_states().
Which versions are affected by CVE-2026-89658?
How do I fix CVE-2026-89658?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-89658 being exploited?
There is no known exploitation of CVE-2026-89658 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-89658, DEBIAN-CVE-2026-89658, GHSA-mr23-3fxm-cw86, UBUNTU-CVE-2026-89658.