McAfee GroupShield for Microsoft Exchange on Exchange Server 2000, and possibly other anti-virus or anti-spam products from McAfee or other vendors, does not scan X- headers for malicious content, which allows remote attackers to bypass virus detection via a crafted message, as demonstrated by a message with an X-Testing header and no message body.
Improper Input Validation The product receives input or data, but it does
not validate or incorrectly validates that the input has the
properties that are required to process the data safely and
correctly.