Logstash 1.5.x before 1.5.3 and 1.4.x before 1.4.4 allows remote attackers to read communications between Logstash Forwarder agent and Logstash server.
https://www.elastic.co/community/security
http://www.securityfocus.com/bid/76015
http://www.securityfocus.com/archive/1/536859/100/0/threaded
http://www.securityfocus.com/archive/1/536050/100/0/threaded
http://packetstormsecurity.com/files/132800/Logstash-1.5.2-SSL-TLS-FREAK.html