MailEnable < 10.54 Reflected XSS in AddressesBcc Parameter of AddressBook.aspx

MailEnable versions prior to 10.54 contain a reflected cross-site scripting (XSS) vulnerability in the AddressesBcc parameter of /Mondo/lang/sys/Forms/AddressBook.aspx. The AddressesBcc value is not properly sanitized when processed via a GET request and is reflected within a <script> block in the JavaScript variable var sAddrBcc. By supplying a crafted payload that terminates the existing LoadCurAddresses() 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 attempts to send an email. Successful exploitation can redirect victims to malicious sites, steal non-HttpOnly cookies, and perform actions as the authenticated user.