A vulnerability in the email message filtering feature of Cisco AsyncOS Software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to cause the CPU utilization to increase to 100 percent, causing a denial of service (DoS) condition on an affected device. The vulnerability is due to improper handling of email messages that contain large attachments. An attacker could exploit this vulnerability by sending a malicious email message through the targeted device. A successful exploit could allow the attacker to cause a permanent DoS condition due to high CPU utilization. This vulnerability may require manual intervention to recover the ESA.