Kbd: local privilege escalation in openvt via incorrect process owner verification allowing passwordless root login

Summary

`openvt -u` is intended to identify the owner of the current VT and then execute `login` as that user from a privileged context. In the documented `kbrequest`/init usage, the ownership test in `authenticate_user()` relies on `stat("/proc/<pid>/fd/0")`. `stat()` on `/proc/<pid>/fd/0` follows the symlink to the underlying TTY device node. As a result, `buf.st_uid` reflects the owner of the TTY node rather than the owner of the process holding the file descriptor. If the TTY owner returns to `root` or the getty owner after logout while an unprivileged process still has `fd 0` attached to that TTY, the check can incorrectly treat that process as belonging to the privileged console owner. Once that check succeeds, the `-u` path executes a passwordless login as the selected user. In the documented `kbrequest`/init deployment using `openvt -us`, this can result in passwordless `login -f root` on the spawned VT. This report establishes that privilege escalation path for that documented deployment; it does not claim equivalent reachability for deployments that do not use `openvt -u` from a privileged `kbrequest`/init path.

Timeline

1. Aug 11, 2026, 8:39 AM UTCCVE published
2. Aug 11, 2026, 5:44 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Oct 9, 2026, 3:46 AM UTCRecord last updated

Affected versions

• kbd

  Version range not reported

• kbd

  Version range not reported

• kbd

  Version range not reported

• openshift/ose-rhel-coreos-9

  Version range not reported

• kbd-main

  Version range not reported

• kbd

  Version range not reported

• kbd

  Version range not reported

• openshift/ose-rhel-coreos-8

  Version range not reported

References 8