The imap_header function in the IMAP functionality for PHP before 4.3.0 allows remote attackers to cause a denial of service via an e-mail message with a large number of "To" addresses, which triggers an error in the rfc822_write_address function.
Argument injection vulnerability in the mail function for PHP 4.x to 4.2.2 may allow attackers to bypass safe mode restrictions and modify command line arguments to the MTA (e.g. sendmail) in the 5th argument to mail(), altering MTA behavior and possibly executing commands.