# CVE-2026-78408: nsenter --join-cgroup privilege escalation via open file descriptor

Source: https://junglewise.ai/threats/cve-2026-78408-nsenter-join-cgroup-privilege-escalation-via-open-file-descriptor  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-02. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-78408 · Severity: high · CVSS 7.9 · Published 2026-09-02

nsenter is a Linux utility used by system administrators to enter namespaces and cgroups for container and process management. A vulnerability in the --join-cgroup option leaves a file descriptor open with root privileges across namespace and credential changes, allowing an unprivileged user to inherit root's ability to move host processes between cgroups. An attacker can exploit this to disrupt critical system services or force termination of unrelated processes running as root.

Vendors: [Util-Linux](https://junglewise.ai/threats/vendors/util-linux).

## Quick answers

**Is CVE-2026-78408 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-78408 being exploited in the wild.

**How severe is CVE-2026-78408?** High severity, with a CVSS score of 7.9, published 2 September 2026.

**Which products and versions are affected?** Util-Linux Nsenter <UNKNOWN>.

**Is there a fix for CVE-2026-78408?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-78408 attacked?** It is attacked with local access.

**Am I affected by CVE-2026-78408?** Check whether you run Util-Linux Nsenter at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in nsenter's --join-cgroup implementation, which opens the target cgroup.procs file as root but fails to close the file descriptor before executing namespace and credential changes via execve(). The kernel's cgroup migration checks rely on credentials captured at open time; because the file descriptor remains open with root credentials, a program running in an attacker-controlled target can inherit and reuse those elevated permissions. An unprivileged user can then migrate and terminate unrelated root processes after a privileged operator uses --join-cgroup against the compromised target. This requires a privileged user to first execute nsenter --join-cgroup against an attacker-controlled namespace, making it a post-exploitation privilege escalation vector rather than a direct remote attack.

## Affected products

- util-linux nsenter <UNKNOWN>

## Timeline

- 2026-09-02: disclosed

## References

- [https://catalog.redhat.com/software/containers/](https://catalog.redhat.com/software/containers/)
- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)