Published: 05 March 2018
Memcached version 1.5.5 contains an Insufficient Control of Network Message Volume (Network Amplification, CWE-406) vulnerability in the UDP support of the memcached server that can result in denial of service via network flood (traffic amplification of 1:50,000 has been reported by reliable sources). This attack appear to be exploitable via network connectivity to port 11211 UDP. This vulnerability appears to have been fixed in 1.5.6 due to the disabling of the UDP protocol by default.
From the Ubuntu security team
It was discovered that Memcached listened to UDP by default. A remote attacker could use this as part of a distributed denial of service attack.
CVSS 3 base score: 7.5
in Ubuntu (and Debian) memcached is bound to the loppback interface by default. However, if memcached is bound to other interfaces, the UDP port is still enabled by default. Ubuntu update is to disable listening on UDP by default. To re-enable UDP, add '-U 11211' to /etc/memcached.conf and restart the memcahced service.