Logjam attack using Diffie-Hellman key exchange.
more info at
https://weakdh.org/
Simple test at
https://weakdh.org/sysadmin.html
or
https://www.ssllabs.com/ssltest
simple fixed
http://serverfault.com/questions/693241/how-to-fix-logjam-vulnerability-in-apache-httpd
:)