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.

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Fixes

Solution

No solution given by the vendor.


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.

History

Thu, 03 Sep 2026 12:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Important


Wed, 02 Sep 2026 10:45:00 +0000

Type Values Removed Values Added
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.
Title Util-linux: util-linux: nsenter --join-cgroup leaks root cgroup migration authority
First Time appeared Redhat
Redhat enterprise Linux
Redhat hummingbird
Redhat openshift
Weaknesses CWE-775
CPEs cpe:/a:redhat:hummingbird:1
cpe:/a:redhat:openshift:4
cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:7
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
Vendors & Products Redhat
Redhat enterprise Linux
Redhat hummingbird
Redhat openshift
References
Metrics cvssV3_1

{'score': 7.9, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:N/I:H/A:H'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: redhat

Published:

Updated: 2026-09-03T12:50:51.689Z

Reserved: 2026-08-24T14:40:14.511Z

Link: CVE-2026-78408

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-02T16:17:23.687

Modified: 2026-09-02T16:17:23.687

Link: CVE-2026-78408

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-02T00:00:00Z

Links: CVE-2026-78408 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-03T12:00:04Z

Weaknesses