Cross-site request forgery (CSRF) vulnerability in compose.php in SquirrelMail 1.4.0 through 1.4.9a allows remote attackers to send e-mails from arbitrary users via certain data in the SRC attribute of an IMG element.
The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.