Unknown vulnerability in Horde IMP 3.2.3 and earlier, before a "security fix," does not properly validate input, which allows remote attackers to execute arbitrary script as other users via script or HTML in an e-mail message, possibly triggering a cross-site scripting (XSS) vulnerability.
https://exchange.xforce.ibmcloud.com/vulnerabilities/16357
http://www.securityfocus.com/bid/10501