Zimbra uses memcached and if not properly configured could lead to a vulnerable system. If you want to read more on memcached attack read this: https://blog.cloudflare.com/memcrashed-major-amplification-attacks-from-port-11211/ How to resolve this vulnerability in 3 steps: Enable firewall on your server Setup zimbra specific rules Bind memcached to localhost Deny memcached port from localhost Let’s start.