If register_globals is on Squirrelmail 1.4.x suffers from a local file inclusion vulnerability.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/46970/Squirrelmail-1.4.x.txt
Source: https://packetstormsecurity.com/files/46970/Squirrelmail-1.4.x.txt.html