A vulnerability in the email message filtering feature of Cisco AsyncOS Software for Cisco Email Security Appliance (ESA) and Cisco Content Security Management Appliance (SMA) could allow an unauthenticated, remote attacker to cause repeated crashes in some internal processes that are running on the affected devices, resulting in a denial of service (DoS) condition. The vulnerability is due to insufficient input validation of email attachments. An attacker could exploit this vulnerability by sending an email message with a crafted attachment through an affected device. A successful exploit could allow the attacker to cause specific processes to crash repeatedly, resulting in the complete unavailability of both the Cisco Advanced Malware Protection (AMP) and message tracking features and in severe performance degradation while processing email. After the affected processes restart, the software resumes filtering for the same attachment, causing the affected processes to crash and restart again. A successful exploit could also allow the attacker to cause a repeated DoS condition. Manual intervention may be required to recover from this situation.