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 roots 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
The product does not release a file descriptor or handle after its effective lifetime has ended, i.e., after the file descriptor/handle is no longer needed.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Red Hat Enterprise Linux 10 | RedHat | util-linux-0:2.40.2-18.el10_2.20 | * |
| Red Hat Hardened Images | RedHat | util-linux-main-2.42.2-3.4.hum1 | * |
| Util-linux | Ubuntu | upstream | * |
Potential Mitigations
- Use resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems.
- When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users.
- Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).
References
- https://access.redhat.com/errata/RHSA-2026:63162
- https://access.redhat.com/errata/RHSA-2026:93461
- https://access.redhat.com/security/cve/CVE-2026-78408
- https://bugzilla.redhat.com/show_bug.cgi?id=2522497
- https://github.com/util-linux/util-linux/security/advisories/GHSA-55fx-f4gg-cfhj
- http://www.openwall.com/lists/oss-security/2026/09/05/2
- https://github.com/util-linux/util-linux/security/advisories/GHSA-55fx-f4gg-cfhj