Roundcube before 1.3.17 and 1.4.x before 1.4.12 is prone to XSS in handling an attachment's filename extension when displaying a MIME type warning message.
An XSS issue was discovered in Roundcube Webmail before 1.2.13, 1.3.x before 1.3.16, and 1.4.x before 1.4.10. The attacker can send a plain text e-mail message, with JavaScript in a link reference element that is mishandled by linkref_addindex in rcube_string_replacer.php.