The remote webmail application is affected by multiple issues.
The installed version of SquirrelMail fails to sanitize user-supplied input to mailbox names before passing them to an IMAP server. An unauthenticated attacker may be able to leverage this issue to launch attacks against the underlying IMAP server or against a user's mailboxes by tricking him into clicking on a specially-formatted link in an email message. There are also reportedly several possible cross-site scripting flaws that could be exploited to inject arbitrary HTML and script code into a user's browser.
Upgrade to version 1.4.7 or higher.