CVE-2026-89686 nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke
A race condition in the Linux kernel NFS server allows remote attackers to cause a denial of service via a BUG_ON crash during concurrent delegation revokes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89686?
CVE-2026-89686 is a critical 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: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke
nfsd4_alloc_layout_stateid reads fp->fi_deleg_file without holding fi_lock when the parent stateid is a delegation. A concurrent delegation revoke via the laundromat can clear fi_deleg_file under fi_lock, causing nfsd_file_get() to return NULL and triggering the BUG_ON.
This race is client-reachable: two NFS clients can trigger it by having one hold a delegation while another opens the same file to force a recall. When the first client doesn't respond to the recall, the laundromat revokes it. A concurrent LAYOUTGET from any client using the delegation stateid hits the race window.
Fix this by taking fi_lock around the fi_deleg_file read in the SC_TYPE_DELEG path, matching the locking discipline of the find_any_file() arm, and replacing the BUG_ON with a graceful error return that cleans up the partially-initialized layout stateid.
Which versions are affected by CVE-2026-89686?
How do I fix CVE-2026-89686?
Apply the vendor's patch.
Is CVE-2026-89686 being exploited?
There is no known exploitation of CVE-2026-89686 in the wild and no public exploit code.
Sources
Also known as AZL-100455, BELL-CVE-2026-89686, DEBIAN-CVE-2026-89686, GHSA-8hmx-j653-mwq6, UBUNTU-CVE-2026-89686.