Bugzilla 2.x through 4.0.x before 4.0.15, 4.1.x and 4.2.x before 4.2.11, 4.3.x and 4.4.x before 4.4.6, and 4.5.x before 4.5.6 does not ensure that a scalar context is used for certain CGI parameters, which allows remote attackers to conduct cross-site scripting (XSS) attacks by sending three values for a single parameter name.