High [CVE-2026-78408] Util-linux: util-linux: nsenter --join-cgroup leaks root cgroup migration authority
This high-severity Red Hat Linux advisory covers CVE-2026-78408 affecting Red Hat Enterprise Linux 10, Red Hat Hardened Images, Red Hat package: libblkid-devel.
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Summary
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.
Affected versions: util-linux v2.40 through v2.42.2. Fixed in v2.41.6 and v2.42.3.
Red Hat severity: Important — CVSS 7.9 (CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:N/I:H/A:H). Weakness: CWE-775.
Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Hardened Images. Red Hat lists Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9; Red Hat OpenShift Container Platform 4 as not affected.
Red Hat does not currently list a fixing RHSA for this CVE.
Affected products named by the advisory: Red Hat package: libblkid-devel; Red Hat package: libfdisk-devel; Red Hat package: libmount-devel; Red Hat package: libsmartcols-devel; and 5 more.
Affected products named by the advisory: Red Hat package: libuuid-devel; Red Hat package: python3-libmount; Red Hat package: util-linux-core; Red Hat package: util-linux.src; and 1 more.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
Mitigation checklist
- 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.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
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