CVE-2026-72693
Received Received - Intake

Privilege Escalation in openvt via TTY Symlink

Publication date: 2026-08-11

Last updated on: 2026-08-11

Assigner: Red Hat, Inc.

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.

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Meta Information

Published
2026-08-11
Last Modified
2026-08-11
Generated
2026-08-11
AI Q&A
2026-08-11
EPSS Evaluated
N/A
NVD
CVE-2026-72693
EUVD
EUVD-2026-55978

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
redhat kbd 2.8.0-3.fc43

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-284 The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.

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Executive Summary

CVE-2026-72693 is a local privilege escalation flaw in the openvt utility from the kbd package. It occurs when openvt -u is used in privileged contexts like kbrequest or init. The vulnerability stems from incorrect process owner verification in the authenticate_user() function. Instead of checking the actual process owner, it relies on the TTY device node owner, which can be manipulated by timing conditions after logout. This allows an unprivileged local attacker to bypass authentication and gain passwordless root login.

Detection Guidance

Check if your system uses openvt -u in privileged init paths like kbrequest. Inspect /etc/inittab or systemd services for openvt -u configurations. Verify if any processes have fd 0 attached to a TTY while the TTY owner is root or getty. Commands: ps -eo pid,tty,comm | grep -E 'openvt|login'; ls -l /proc/*/fd/0 2>/dev/null | grep /dev/tty; stat -c '%U' /proc/*/fd/0 2>/dev/null.

Impact Analysis

If your system uses openvt -u in a privileged kbrequest or init deployment, an attacker with local access could exploit this to gain root privileges without a password. This could lead to full system compromise, allowing the attacker to install malware, steal data, or perform other malicious actions. Exploitation requires specific non-default configurations and timing conditions.

Compliance Impact

This vulnerability could lead to unauthorized root access, potentially violating data confidentiality and integrity requirements in GDPR and HIPAA. If exploited, it may result in unauthorized data access, modification, or exfiltration, leading to compliance violations. Organizations using affected configurations should mitigate this risk to maintain regulatory compliance.

Mitigation Strategies

Disable openvt -u in privileged init paths like kbrequest. Replace with standard authenticated login or disable keyboard request bindings. Update kbd package if a fix is released. Monitor for unauthorized root logins via openvt. Commands: sed -i 's/openvt -u/openvt/' /etc/inittab; systemctl daemon-reload; systemctl restart systemd-logind.

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