What’s Vulnerable › Vulnerabilities

CVE-2026-72693: Kbd: local privilege escalation in openvt via incorrect process owner verification allowing passwordless root login

Description

`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.

Affected products

How to fix

Upgrade to a fixed version: Red Hat Enterprise Linux 10 0:2.6.4-8.el10_2; Red Hat Enterprise Linux 8 0:2.0.4-11.el8_10.1; Red Hat Enterprise Linux 9 0:2.4.0-12.el9_8; Red Hat Hardened Images 2.10.0-2.hum1; Red Hat OpenShift Container Platform 4.22 4.22.9.8.202608251819-0, 4.22.9.8.202609081748-0. Check the vendor advisory for mitigations.

References

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