# CVE-2026-78408: Util-linux: util-linux: nsenter --join-cgroup leaks root cgroup migration authority

> An attacker can exploit nsenter to inherit root cgroup migration authority, allowing them to move or terminate unrelated root processes.

- **Severity:** High 7.9 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:N/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:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 2 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** ALPINE-CVE-2026-78408, AZL-99393, BELL-CVE-2026-78408, DEBIAN-CVE-2026-78408, ECHO-3f6d-9602-8caa, ROOT-OS-DEBIAN-12-CVE-2026-78408, ROOT-OS-DEBIAN-13-CVE-2026-78408, UBUNTU-CVE-2026-78408

## What is CVE-2026-78408?

CVE-2026-78408 is a high-severity vulnerability in Red Hat Enterprise Linux 10, published on 2 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

The nsenter --join-cgroup option opens the target cgroup.procs file as root and leaves that file descriptor open across later namespace and credential changes and across execve(). Because the kernel checks later cgroup migrations using the credentials from the original open, a program run in an attacker-controlled target can inherit root's ability to move host processes between cgroups. After a privileged operator uses --join-cgroup against that target, an unprivileged user can migrate and terminate unrelated root processes.

Weakness: CWE-775 (Missing Release of File Descriptor or Handle after Effective Lifetime)

## Which versions are affected by CVE-2026-78408?


## How do I fix CVE-2026-78408?

Apply the vendor's patch.

## Is CVE-2026-78408 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-78408 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-78408 and fix it if it is affected.

What it is: CVE-2026-78408 is a high-severity vulnerability in Red Hat Enterprise Linux 10, published on 2 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-78408 exists.

Affected product: Red Hat Enterprise Linux 10. 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-2026-78408/ (Markdown: https://insights.sbomify.com/CVE-2026-78408/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-78408
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-78408
- OSV: https://osv.dev/vulnerability/CVE-2026-78408

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-78408/
Summaries are generated and may contain mistakes; the official description above is the record.