CVE-2026-89685 nfsd: fix clock domain mismatch in clients_still_reclaiming()
A clock domain mismatch in the Linux kernel NFS server allows attackers to indefinitely block non-reclaim operations, causing 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-2026-89685?
CVE-2026-89685 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: fix clock domain mismatch in clients_still_reclaiming()
clients_still_reclaiming() computes a deadline from nn->boot_time (CLOCK_REALTIME, ~1.7 billion) but compares it against ktime_get_boottime_seconds() (CLOCK_BOOTTIME, seconds since boot). The comparison is always false — it would take ~54 years of uptime for BOOTTIME to exceed the REALTIME-derived deadline.
This means any client can hold the server in grace indefinitely by sending CLAIM_PREVIOUS OPEN requests, blocking all non-reclaim operations for all other clients.
Add boot_time_bt (CLOCK_BOOTTIME) alongside the existing boot_time and use it for the deadline computation. boot_time (CLOCK_REALTIME) is preserved for its cl_boot clientid-nonce role.
Which versions are affected by CVE-2026-89685?
How do I fix CVE-2026-89685?
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-2026-89685 being exploited?
There is no known exploitation of CVE-2026-89685 in the wild and no public exploit code.
Sources
Also known as AZL-100544, BELL-CVE-2026-89685, DEBIAN-CVE-2026-89685, GHSA-3574-3v33-rcrf, UBUNTU-CVE-2026-89685.