functions/mime.php in SquirrelMail before 1.4.18 does not protect the application's content from Cascading Style Sheets (CSS) positioning in HTML e-mail messages, which allows remote attackers to spoof the user interface, and conduct cross-site scripting (XSS) and phishing attacks, via a crafted message.
Cross-site scripting (XSS) vulnerability in SquirrelMail before 1.4.17 allows remote attackers to inject arbitrary web script or HTML via a crafted hyperlink in an HTML part of an e-mail message.
SquirrelMail 1.4.11 and 1.4.12, as distributed on sourceforge.net before 20071213, has been externally modified to create a Trojan Horse that introduces a PHP remote file inclusion vulnerability, which allows remote attackers to execute arbitrary code.