MailEnable versions prior to 10.54 contain a reflected cross-site scripting (XSS) vulnerability in the Id parameter of /Mobile/ContactDetails.aspx. The Id value is not properly sanitized when processed via a GET request and is reflected within a <script> block in the response. By supplying a crafted payload that terminates an existing JavaScript function, inserts attacker-controlled script, and comments out remaining code, a remote attacker can execute arbitrary JavaScript in a victim’s browser when the victim opens a malicious link. Successful exploitation can redirect victims to malicious sites, steal cookies not protected by HttpOnly, inject arbitrary HTML or CSS, and perform actions as the authenticated user.