# CVE-2026-64556: perf/core: Detach event groups during remove_on_exec

> A race condition in the Linux kernel perf subsystem can corrupt PMU context lists, leading to a system crash or denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-94139, BELL-CVE-2026-64556, DEBIAN-CVE-2026-64556, GHSA-mpx2-cmqf-859j, ROOT-OS-DEBIAN-12-CVE-2026-64556, UBUNTU-CVE-2026-64556

## What is CVE-2026-64556?

CVE-2026-64556 is a high-severity vulnerability in Linux, published on 29 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:

perf/core: Detach event groups during remove_on_exec

perf_event_remove_on_exec() removes events by calling
perf_event_exit_event(). For top-level events, this removes the event from
the context with DETACH_EXIT only.

This can leave inconsistent group state when a removed event is a group
leader and the group contains siblings without remove_on_exec. If the group
was active, the surviving siblings can remain active and attached to the
removed leader's sibling list, but are no longer represented by a valid
group leader on the PMU context active lists.

A later close of the removed leader uses DETACH_GROUP and can promote the
still-active siblings from this stale group state. The next schedule-in can
then add an already-linked active_list entry again, corrupting the PMU
context active list.

With DEBUG_LIST enabled, this is caught as a list_add double-add in
merge_sched_in().

Fix this by detaching group relationships when remove_on_exec removes an
event. This preserves the existing task-exit and revoke behavior, while
ensuring surviving siblings are ungrouped before the removed event leaves
the context.

Weakness: CWE-662 (Improper Synchronization)

## Which versions are affected by CVE-2026-64556?


## How do I fix CVE-2026-64556?

Apply the vendor's patch.

## Is CVE-2026-64556 being exploited?

There is no known exploitation of CVE-2026-64556 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64556 and fix it if it is affected.

What it is: CVE-2026-64556 is a high-severity vulnerability in Linux, published on 29 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-2026-64556 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-2026-64556/ (Markdown: https://insights.sbomify.com/CVE-2026-64556/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64556
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64556
- OSV: https://osv.dev/vulnerability/CVE-2026-64556

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64556/
Summaries are generated and may contain mistakes; the official description above is the record.