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

Status: published. Published: 2026-09-02. Updated: 2026-11-02.

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.

## Remediation

- workaround: Upgrade to util-linux v2.41.6, v2.42.3, or later. Until a fix is applied, do not run nsenter --join-cgroup (including nsenter --target PID --all --join-cgroup) against untrusted processes or namespaces. The fix closes the cgroup.procs descriptor immediately after joining, and opens it with O_CLOEXEC. (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat Enterprise Linux 10 (util-linux): ≥ 0:2.40.2-18.el10_2.20; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Hardened Images (util-linux-main): ≥ 2.42.2-3.4.hum1; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (util-linux): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (util-linux): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (rhel8/flatpak-runtime): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (rhel8/flatpak-sdk): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (util-linux): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-8): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 5 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 7.9 (high); CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:N/I:H/A:H; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 0.19% as of 2026-11-01; percentile 9.06%

- SSVC: exploitation poc; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-775

## Exploit evidence

- exploit: https://github.com/util-linux/util-linux/security/advisories/GHSA-55fx-f4gg-cfhj (ADP: CISA-ADP)

## References

- https://access.redhat.com/errata/RHSA-2026:63162 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:93461 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2026-78408 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2522497 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://github.com/util-linux/util-linux/security/advisories/GHSA-55fx-f4gg-cfhj (CNA: redhat)

- https://github.com/util-linux/util-linux/security/advisories/GHSA-55fx-f4gg-cfhj (ADP: CISA-ADP; exploit)

- http://www.openwall.com/lists/oss-security/2026/09/05/2 (ADP: CVE)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-78408; retrieved 2026-11-02; source updated 2026-11-02

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-78408; retrieved 2026-11-02; source updated Not reported

Revision: f93381c9ac69faf5fb63cc213f80856342c7054273a292411f0dfc58a0687f4a

Canonical: https://y2.dev/cve/CVE-2026-78408