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

Descripción

`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.

Datos: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Se publican tal como los indican las fuentes, en inglés.

Productos y versiones afectados

Referencias y parches

• RHSA-2026:41136 vendor-advisory
• RHSA-2026:57597 vendor-advisory
• RHSA-2026:57610 vendor-advisory
• RHSA-2026:60440 vendor-advisory
• RHSA-2026:66357 vendor-advisory
• RHSA-2026:78951 vendor-advisory
• https://access.redhat.com/security/cve/CVE-2026-72693 vdb-entry
• RHBZ#2462115 issue-tracking