CVE-2026-89705 nfsd: restore rq_status_counter to even on all nfsd_dispatch() exit paths
A race condition in the Linux kernel NFS server allows a lockless reader to access mutating fields, potentially causing out-of-bounds reads and system instability.
- 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
What is CVE-2026-89705?
CVE-2026-89705 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:
nfsd: restore rq_status_counter to even on all nfsd_dispatch() exit paths
nfsd_dispatch() sets rq_status_counter to an odd value once a request has been decoded, and back to an even value once it has been fully processed, forming a seq-lock like protocol with the lockless reader in nfsd_nl_rpc_status_get_dumpit().
Only the fully successful path restored the counter to even. The cache-hit (RC_REPLY), drop (RC_DROPIT / RQ_DROPME) and encode-error paths all return after the odd-valued store without ever bringing the counter back to even. Once one of those paths is taken, rq_status_counter is left odd: the next request's decode ORs in 1 (still odd) and only a subsequent successful encode restores even. While stuck odd, the dumpit reader treats the rqstp fields as stable and its retry check compares against the same unchanging odd value, so it never detects concurrent mutation. This exposes actively mutating fields (e.g. args->ops / args->opcnt during compound decode and release) to the lockless reader, which can read past the end of the 8-element inline ops array.
Add a helper that advances the counter to the next even value and call it on every return path that follows the odd-valued store. The decode-error path is left untouched as it is reached before the counter is set odd.
Which versions are affected by CVE-2026-89705?
How do I fix CVE-2026-89705?
Apply the vendor's patch.
Is CVE-2026-89705 being exploited?
There is no known exploitation of CVE-2026-89705 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-89705, DEBIAN-CVE-2026-89705, GHSA-pvqx-hghh-c66m, UBUNTU-CVE-2026-89705.