CVE-2026-89691 nfsd: clear opcnt on compound arg release to prevent OOB read
An out-of-bounds read in the Linux kernel NFS server allows leaking adjacent slab memory to userspace via netlink due to stale operation counts.
- 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-2026-89691?
CVE-2026-89691 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: clear opcnt on compound arg release to prevent OOB read
nfsd4_release_compoundargs() resets args->ops to the inline iops[8] array when the dynamically-allocated ops buffer is freed, but leaves args->opcnt at its original value (which can be up to 200 for NFSv4.1+ compounds).
If rq_status_counter is stuck at an odd value (which can happen when nfsd_dispatch() hits an error path after setting it odd), the RPC status dumpit handler reads min(opcnt, 16) entries from args->ops[]. Since iops only has 8 elements and is the last field in struct nfsd4_compoundargs, reading indices 8-15 accesses adjacent slab memory and leaks it to userspace via netlink.
Zero opcnt unconditionally in nfsd4_release_compoundargs() so stale compound metadata is never exposed through the status interface.
[ cel: Remove the kvfree_rcu_mightsleep() sleep from the exposure window ]
Which versions are affected by CVE-2026-89691?
How do I fix CVE-2026-89691?
Apply the vendor's patch.
Is CVE-2026-89691 being exploited?
There is no known exploitation of CVE-2026-89691 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-89691, DEBIAN-CVE-2026-89691, GHSA-v764-gh88-p9gg, UBUNTU-CVE-2026-89691.