Summary: Logstash 1.5.3 and prior versions are vulnerable to a SSL/TLS security issue which allows an attacker to successfully implement a man in the middle attack. This vulnerability is not present in the initial installation of Logstash. This insecurity is exposed when users configure Lumberjack output to connect two Logstash instances. In such deployments, a Logstash instance is used to collect logs from a webserver and securely transmit them to a central Logstash instance to perform additional filtering and storing. Note: Communication between Logstash Forwarder and Lumberjack Input in Logstash is not affected by this vulnerability. We have been assigned CVE-2015-5619 for this issue. Fixed versions: Version 1.5.4 and 1.4.5 has been patched with a fix that addresses this vulnerability. Remediation: Users that currently use Logstash with the Lumberjack output or may want to use it in the future should upgrade to 1.5.4 or 1.4.5. Users that do not want to upgrade can address the vulnerability by disabling the Lumberjack output. Credit: Markus Frosch reported this issue. CVSS Overall CVSS score: 4.3