As per default configuration, memcached on CentOS 6 and CentOS 7 listens on all IPs and thus is accessible from outside if your server’s firewall is not restrictive by default.
You can secure memcached by editing the file
/etc/sysconfig/memcached and replacing the line
Then restart memcached,
service memcached restart
New installations will configure memcached to listen on only localhost.