OpenBSD 6.6, in a non-default configuration where S/Key or YubiKey authentication is enabled, allows local users to become root by leveraging membership in the auth group. This occurs because root's file can be written to /etc/skey or /var/db/yubikey, and need not be owned by root.

References

• https://nvd.nist.gov/vuln/detail/CVE-2019-19522
• https://seclists.org/bugtraq/2019/Dec/8
• https://www.openbsd.org/errata66.html
• https://www.openwall.com/lists/oss-security/2019/12/04/5
• http://packetstormsecurity.com/files/155572/Qualys-Security-Advisory-OpenBSD-Authentication-Bypass-Privilege-Escalation.html
• http://seclists.org/fulldisclosure/2019/Dec/14
• http://www.openwall.com/lists/oss-security/2019/12/04/5