# CVE-2026-93099: fs/resctrl: Fix UAF from worker threads when domains are removed

> A use-after-free in the Linux kernel resctrl subsystem allows local attackers to execute arbitrary code or escalate privileges via race conditions during CPU hotplug.

- **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:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101933, BELL-CVE-2026-93099, DEBIAN-CVE-2026-93099, GHSA-qpj7-xpxx-33h9, UBUNTU-CVE-2026-93099

## What is CVE-2026-93099?

CVE-2026-93099 is an use after free vulnerability in Linux, published on 17 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:

fs/resctrl: Fix UAF from worker threads when domains are removed

The mbm_handle_overflow() and cqm_handle_limbo() workers read event counters
and may sleep while doing so. They are scheduled via delayed_work embedded in
struct rdt_l3_mon_domain. Architecture allocates and frees these domains from
CPU hotplug callbacks under cpus_write_lock(), and the workers acquire
cpus_read_lock() to keep the domain alive across their access.

A use-after-free can occur when a worker is blocked waiting for
cpus_read_lock() while the hotplug core holds cpus_write_lock(): the
architecture frees the rdt_l3_mon_domain that contains the worker's
work_struct. When the worker unblocks, the container_of() it performs on the
embedded work pointer dereferences freed memory.

Drop cpus_read_lock() from the workers and instead drain pending and in-flight
work synchronously before the architecture can free the domain.  Since
architecture offlines the domain under cpus_write_lock() after it has been
unlinked from the RCU list and a grace period has elapsed, no new work can be
scheduled. The cancel only needs to wait out existing work.  Drop
rdtgroup_mutex during CPU offline around cancel_delayed_work_sync() so that
a worker waiting on the mutex can complete before re-pinning the work on
a different CPU.

When offlining a CPU the architecture may iterate over resources in any order.
For example, the MBA control domain may be offlined before or after
a corresponding L3 monitor domain. Ensure that resctrl fs cancels the workers
no matter what order the architecture offlines the domains.

## Which versions are affected by CVE-2026-93099?


## How do I fix CVE-2026-93099?

Apply the vendor's patch.

## Is CVE-2026-93099 being exploited?

There is no known exploitation of CVE-2026-93099 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93099 and fix it if it is affected.

What it is: CVE-2026-93099 is an use after free vulnerability in Linux, published on 17 Sep 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-2026-93099 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-2026-93099/ (Markdown: https://insights.sbomify.com/CVE-2026-93099/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93099
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93099
- OSV: https://osv.dev/vulnerability/CVE-2026-93099

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-93099/
Summaries are generated and may contain mistakes; the official description above is the record.