Cross-site scripting (XSS) vulnerability in the Login form in Piwik 0.1.6 through 0.5.5 allows remote attackers to inject arbitrary web script or HTML via the form_url parameter.
http://www.vupen.com/english/advisories/2010/1079
http://www.openwall.com/lists/oss-security/2010/05/05/4
http://www.openwall.com/lists/oss-security/2010/05/05/3