(1) Webmin 0.96 and (2) Usermin 0.90 with password timeouts enabled allow local and possibly remote attackers to bypass authentication and gain privileges via certain control characters in the authentication information, which can force Webmin or Usermin to accept arbitrary username/session ID combinations.
http://www.securityfocus.com/bid/4700
http://www.linux-mandrake.com/en/security/2002/MDKSA-2002-033.php