CVE-2026-89714 NFS: fix delegation_hash_table leak when nfs4_server_common_setup() fails
A memory leak in the Linux kernel NFS client allows local attackers to exhaust kernel memory by repeatedly failing NFSv4 mounts, causing denial of service.
- 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-2026-89714?
CVE-2026-89714 is a memory corruption 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:
NFS: fix delegation_hash_table leak when nfs4_server_common_setup() fails
nfs4_server_common_setup() allocates server->delegation_hash_table first, but server->destroy - the only path that frees the table via nfs4_destroy_server() - is not assigned until the very end of the function. If any intermediate step fails (the is_ds_only_client() check, nfs4_init_session(), nfs4_get_rootfh(), or nfs_probe_server()), the function returns with server->destroy still NULL, so the caller's nfs_free_server() skips the destroy callback and the hash table is leaked (4 KiB per attempt with the default delegation watermark).
This is trivially reachable from userspace: every failed NFSv4 mount leaks one allocation. A client that persistently retries a mount that cannot succeed leaks kernel memory without bound. Observed in production where a Longhorn backup poller retried mount.nfs4 against an NFSv3-only server roughly 10 times per second, leaking ~3.4 GiB of unreclaimable slab (kmalloc-rnd-13-4k) per day; the node accumulated 12 GiB of leaked slab before the source was identified via the kmem:kmalloc tracepoint (call_site=nfs4_delegation_hash_alloc).
Reproducer:
# server exports NFSv3 only (or export path absent for v4) while :; do mount -t nfs4 <server>:/missing /mnt; done # watch SUnreclaim in /proc/meminfo grow 4 KiB per iteration
Free the table on the error paths between the allocation and the assignment of server->destroy.
Which versions are affected by CVE-2026-89714?
How do I fix CVE-2026-89714?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-89714 being exploited?
There is no known exploitation of CVE-2026-89714 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-89714, DEBIAN-CVE-2026-89714, GHSA-hv3g-87gw-4m9v, UBUNTU-CVE-2026-89714.