CVE-2026-64477 x86,fs/resctrl: Prevent out-of-bounds access while offlining CPU when SNC enabled
A local attacker can trigger an out-of-bounds memory access in the Linux kernel resctrl subsystem during CPU offlining on SNC-enabled systems, causing a crash or information leak.
- 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-2026-64477?
CVE-2026-64477 is a memory corruption vulnerability in Linux, published on 25 Jul 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:
x86,fs/resctrl: Prevent out-of-bounds access while offlining CPU when SNC enabled
The architecture updates the cpu_mask in a domain's header to track which online CPUs are associated with the domain. When this mask becomes empty the architecture initiates offline of the domain that includes calling on resctrl fs to offline the domain. If it is a monitoring domain in which LLC occupancy is tracked resctrl fs forces the limbo handler to clear all busy RMID state associated with the domain.
The limbo handler always reads the current event value associated with a busy RMID irrespective of it being checked as part of regular "is it still busy" check or whether it will be forced released anyway. When reading an RMID on a system with SNC enabled the "logical RMID" is converted to the "physical RMID" and this conversion requires the NUMA node ID of the resctrl monitoring domain that is in turn determined by querying the NUMA node ID of any CPU belonging to the monitoring domain.
When the monitoring domain is going offline its cpu_mask is empty causing the NUMA node ID query via cpu_to_node() to be done with "nr_cpu_ids" as argument resulting in an out-of-bounds access.
Refactor the limbo handler to skip reading the RMID when the RMID will just be forced to no longer be dirty in the domain anyway. Add a safety check to the architecture's RMID reader to protect against this scenario.
Which versions are affected by CVE-2026-64477?
How do I fix CVE-2026-64477?
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-2026-64477 being exploited?
There is no known exploitation of CVE-2026-64477 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-64477, DEBIAN-CVE-2026-64477, GHSA-72f8-7m2r-7r88, ROOT-OS-UBUNTU-2204-CVE-2026-64477, UBUNTU-CVE-2026-64477.