Cisco fixed two denial-of-service (DoS) flaws in Email Security Appliance products that can be exploited by a remote unauthenticated attacker. The first flaw tracked as CVE-2018-15453 has been rated as critical, it is a memory corruption bug caused by improper input validation in emails signed with Secure/Multipurpose Internet Mail Extensions (S/MIME) The second flaw affects the message filtering feature of AsyncOS software. There is no evidence of malicious exploitation.”]
Source: https://securityaffairs.co/wordpress/79737/security/cisco-esa-dos-flaw.html