CVE-2026-22989 nfsd: check that server is running in unlock_filesystem
A local attacker can crash the NFS server by triggering a null pointer dereference when unlocking the filesystem while the server is not running.
- 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-2026-22989?
CVE-2026-22989 is a medium-severity vulnerability in Linux kernel, published on 23 Jan 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: check that server is running in unlock_filesystem
If we are trying to unlock the filesystem via an administrative interface and nfsd isn't running, it crashes the server. This happens currently because nfsd4_revoke_states() access state structures (eg., conf_id_hashtbl) that has been freed as a part of the server shutdown.
[ 59.465072] Call trace: [ 59.465308] nfsd4_revoke_states+0x1b4/0x898 [nfsd] (P) [ 59.465830] write_unlock_fs+0x258/0x440 [nfsd] [ 59.466278] nfsctl_transaction_write+0xb0/0x120 [nfsd] [ 59.466780] vfs_write+0x1f0/0x938 [ 59.467088] ksys_write+0xfc/0x1f8 [ 59.467395] __arm64_sys_write+0x74/0xb8 [ 59.467746] invoke_syscall.constprop.0+0xdc/0x1e8 [ 59.468177] do_el0_svc+0x154/0x1d8 [ 59.468489] el0_svc+0x40/0xe0 [ 59.468767] el0t_64_sync_handler+0xa0/0xe8 [ 59.469138] el0t_64_sync+0x1ac/0x1b0
Ensure this can't happen by taking the nfsd_mutex and checking that the server is still up, and then holding the mutex across the call to nfsd4_revoke_states().
Which versions are affected by CVE-2026-22989?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-22989?
Apply the vendor's patch.
Is CVE-2026-22989 being exploited?
There is no known exploitation of CVE-2026-22989 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-22989, DEBIAN-CVE-2026-22989, GHSA-rph5-qwhf-vw4p, ROOT-OS-DEBIAN-13-CVE-2026-22989, UBUNTU-CVE-2026-22989.