Text_Filter/lib/Horde/Text/Filter/Xss.php in Horde Application Framework before 3.3.6 Horde Groupware before 1.2.5 and Horde Groupware Webmail Edition before 1.2.5 does not properly handle data: URIs which allows remote attackers to conduct cross-site scripting (XSS) attacks via data:text/html values for the HREF attribute of an A element in an HTML e-mail message. NOTE: the vendor states that the issue is caused by \an XSS vulnerability in Firefox browsers.\