A vulnerability in certain attachment detection mechanisms of the Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to bypass the filtering functionality of an affected device. The vulnerability is due to improper detection of certain content sent to an affected device. An attacker could exploit this vulnerability by sending certain file types without Content-Disposition information to an affected device. A successful exploit could allow an attacker to send messages that contain malicious content to users.