# 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.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Jul 2026
- **Updated:** 17 Aug 2026
- **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

## 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.

## Is CVE-2026-64477 being exploited?

There is no known exploitation of CVE-2026-64477 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64477 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-64477 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-64477/ (Markdown: https://insights.sbomify.com/CVE-2026-64477/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64477
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64477
- OSV: https://osv.dev/vulnerability/CVE-2026-64477

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64477/
Summaries are generated and may contain mistakes; the official description above is the record.