Plugin/passwordauth.pm (aka the passwordauth plugin) in ikiwiki 1.34 through 2.47 allows remote attackers to bypass authentication, and login to any account for which an OpenID identity is configured and a password is not configured, by specifying an empty password during the login sequence.
https://exchange.xforce.ibmcloud.com/vulnerabilities/42798
http://www.vupen.com/english/advisories/2008/1710
http://www.securityfocus.com/bid/29479
http://www.openwall.com/lists/oss-security/2008/05/31/3
http://secunia.com/advisories/30468
http://ikiwiki.info/security/#index33h2