CVE-2026-89692 nfsd: clear CALLBACK_RUNNING on failed delegation recall queue
A logic error in the Linux kernel NFS server leaves a flag set on failed recall attempts, causing subsequent delegations to stall and leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89692?
CVE-2026-89692 is a high-severity denial of service 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: clear CALLBACK_RUNNING on failed delegation recall queue
nfsd_break_one_deleg() sets NFSD4_CALLBACK_RUNNING via test_and_set_bit at entry to serialize recall work, then calls nfsd4_run_cb() to queue the recall. When the queue attempt fails the refcount bump is undone, but the RUNNING bit is left set. The only site that clears the bit is nfsd41_destroy_cb() (fs/nfsd/nfs4callback.c), which runs from the workqueue and is therefore unreachable when nothing was queued.
The bit becomes a permanent latch on dp->dl_recall.cb_flags: every subsequent break_lease() on the same delegation hits the early-return guard in nfsd_break_one_deleg() and silently skips the recall, so the delegation is never broken and the conflicting open or lock stalls.
Fix by clearing NFSD4_CALLBACK_RUNNING on the !queued branch alongside the refcount_dec.
Which versions are affected by CVE-2026-89692?
How do I fix CVE-2026-89692?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-89692 being exploited?
There is no known exploitation of CVE-2026-89692 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-89692, DEBIAN-CVE-2026-89692, GHSA-mcqc-fm6v-5h2r, UBUNTU-CVE-2026-89692.