A vulnerability in the malware detection functionality within Advanced Malware Protection (AMP) of Cisco AsyncOS Software for Cisco Email Security Appliances (ESAs) could allow an unauthenticated, remote attacker to cause an email attachment containing malware to be delivered to the end user. The vulnerability is due to the failure of AMP to scan certain EML attachments that could contain malware. An attacker could exploit this vulnerability by sending an email with a crafted EML attachment through the targeted device. A successful exploit could allow the attacker to bypass the configured ESA email message and content filtering and allow the malware to be delivered to the end user. Vulnerable Products: This vulnerability affects Cisco AsyncOS Software for Cisco ESA, both virtual and hardware appliances, that are configured with message or content filters to scan incoming email attachments on the ESA. Cisco Bug IDs: CSCuz81533.