SSL (secure sockets layer) and its modern incarnation TLS (transport layer security) constitute the S in HTTPS, and form the basis of online web security. In 2009, Moxie Marlinspike presented a paper at the Black Hat conference in Las Vegas in which he outlined a number of attacks against SSL. He did this by sneaking a [NUL] character (a byte with the numeric value of zero) into the name on the digital signature, something like this:. This means you now have a way to let domain.test mint certificates that look as though they belong to example.org.”]
Source: https://nakedsecurity.sophos.com/2013/06/30/ruby-openssl-sprintf-2009-style-man-in-the-middle/