CVE-2026-90039 NFSD: Guard admin state-revocation walks with NFSD_NET_UP
A local administrator can crash the Linux kernel by triggering NFS state revocation before server threads start, causing a null pointer dereference.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90039?
CVE-2026-90039 is a vulnerability in Linux, published on 16 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: Guard admin state-revocation walks with NFSD_NET_UP
Writing to /proc/fs/nfsd/unlock_filesystem, or sending the NFSD_CMD_UNLOCK_FILESYSTEM or NFSD_CMD_UNLOCK_EXPORT netlink command, walks the NFSv4 client hash tables to revoke open state and cancel async COPY operations. All three handlers gate that walk on nn->nfsd_serv, but a listener added via portlist or netlink listener_set sets nn->nfsd_serv before any nfsd thread starts. nfsd_startup_net() has not yet allocated nn->conf_id_hashtbl, so the walkers dereference a NULL table. A local administrator with CAP_SYS_ADMIN can crash the kernel this way without ever starting the server.
nn->nfsd_serv is set when the service is created, which precedes table allocation. NFSD_NET_UP instead brackets the window where the tables are live: set at the end of nfsd_startup_net() and cleared in nfsd_shutdown_net() after they are freed, both under nfsd_mutex. Gating the three unlock paths on NFSD_NET_UP fixes the startup-time NULL dereference while preserving the earlier post-shutdown use-after-free fix.
Which versions are affected by CVE-2026-90039?
How do I fix CVE-2026-90039?
Apply the vendor's patch.
Is CVE-2026-90039 being exploited?
There is no known exploitation of CVE-2026-90039 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-90039, DEBIAN-CVE-2026-90039, GHSA-m7r7-c74x-x286, UBUNTU-CVE-2026-90039.