PHP 4.0.5 through 4.1.0 in safe mode does not properly cleanse the 5th parameter to the mail() function, which allows local users and possibly remote attackers to execute arbitrary commands via shell metacharacters.
Improper Neutralization of Argument Delimiters in a Command The product constructs a string for a command to be executed by a separate component
in another control sphere, but it does not properly delimit the
intended arguments, options, or switches within that command string.