We first read about memcached DDoS attacks when on February 28, 2018, the code hosting website GitHub was hit by the largest-ever DDoS attack that peaked at 1.3Tbps.

Memcached is a free and open source, high-performance, distributed memory caching system designed to speed up dynamic web applications by alleviating database load.

Clients communicate with memcached servers via TCP or UDP on port 11211.

The abuse of memcached servers in DDoS Attacks is quite simple, the attacker sends a request to the targeted server on port 11211 spoofing the IP address of the victim. In a memcached DDoS attack, the request sent to the server is composed of a few bytes, while the response can be tens of thousands of times bigger, resulting in an amplification attack.

Experts at Cloudflare dubbed this type of attack Memcrashed, according to the researcher the amplification technique could allow attackers to obtain an amplification factor of 51,200.

Cloudflare recommends disabling UDP support unless it’s needed and isolating memcached servers from the Internet. Internet service providers have to fix vulnerable protocols and prevent IP spoofing.

“Internet Service Providers – In order to defeat such attacks in future, we need to fix vulnerable protocols and also IP spoofing. As long as IP spoofing is permissible on the internet, we’ll be in trouble.” concluded Cloudflare.

“Developers – Please please please: Stop using UDP. If you must, please don’t enable it by default. If you do not know what an amplification attack is I hereby forbid you from ever typing SOCK_DGRAM into your editor.”

The fear for this new kind of attack represents a good opportunity for cyber criminals, crooks already started to blackmail companies asking for a ransom demand in Monero cryptocurrency to avoid being attacked via Memcached servers.