Bug#1144392: kdb: CVE-2026-72693

Source: kdb
X-Debbugs-CC: [email protected]
Severity: grave
Tags: security

Hi,

The following vulnerability was published for kdb.

CVE-2026-72693[0]:
| `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.

https://bugzilla.redhat.com/show_bug.cgi?id=2462115
Fixed by: https://github.com/legionus/kbd/commit/78d5ae119742e87baa7dbe0f5c4107e7533fd698 (v2.10.0)


If you fix the vulnerability please also make sure to include the
CVE (Common Vulnerabilities & Exposures) id in your changelog entry.

For further information see:

[0] https://security-tracker.debian.org/tracker/CVE-2026-72693
    https://www.cve.org/CVERecord?id=CVE-2026-72693

Please adjust the affected versions in the BTS as needed.