CVE-2026-89604 efivarfs: Rate limit statfs() handler
Unprivileged local users can cause a denial of service by flooding the efivarfs statfs handler, triggering expensive SMM operations on x86 systems.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89604?
CVE-2026-89604 is a denial of service 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:
efivarfs: Rate limit statfs() handler
Ravi reports that statfs() may be called by unprivileged users on the efivarfs mount point, which may result in a flood of calls to the QueryVariableInfo() runtime service. These calls are disproportionately costly on x86 systems where the variable store is backed by SMM, as each SMM entry requires a rendez-vous of all the CPUs.
So rate limit the calls to QueryVariableInfo() at twice per second, and return the most recently obtained value for calls that are elided.
Which versions are affected by CVE-2026-89604?
How do I fix CVE-2026-89604?
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-2026-89604 being exploited?
There is no known exploitation of CVE-2026-89604 in the wild and no public exploit code.
Sources
Also known as AZL-100856, BELL-CVE-2026-89604, DEBIAN-CVE-2026-89604, GHSA-pmmg-3c8m-93q3, UBUNTU-CVE-2026-89604.