MIMEDefang in MIME-tools 5.414 allows remote attackers to bypass virus scanning capabilities via an e-mail attachment with a virus that contains an empty boundary string in the Content-Type header.

SMTP content filter engines, including (1) GFI MailSecurity for Exchange/SMTP before 7.2, (2) InterScan VirusWall before 3.52 build 1494, (3) the default configuration of MIMEDefang before 2.21, and possibly other products, do not detect fragmented emails as defined in RFC2046 ("Message Fragmentation and Reassembly") and supported in such products as Outlook Express, which allows remote attackers to bypass content filtering, including virus checking, via fragmented emails of the message/partial content type.