A vulnerability in the email message scanning of Cisco AsyncOS Software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to bypass configured filters on the device. The vulnerability is due to improper input validation of certain email fields. An attacker could exploit this vulnerability by sending a crafted email message to a recipient protected by the ESA. A successful exploit could allow the attacker to bypass configured message filters and inject arbitrary scripting code inside the email body. The malicious code is not executed by default unless the recipient’s email client is configured to execute scripts contained in emails.