(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.
Directory traversal vulnerability in edit_action.cgi of Webmin Directory 0.91 allows attackers to gain privileges via a '..' (dot dot) in the argument.
Webmin 0.84 and earlier does not properly clear the HTTP_AUTHORIZATION environment variable when the web server is restarted, which makes authentication information available to all CGI programs and allows local users to gain privileges.
Webmin before 0.5 does not restrict the number of invalid passwords that are entered for a valid username, which could allow remote attackers to gain privileges via brute force password cracking.