Resin is the Java Application Server for high traffic sites that require speed and scalability. It is one of the earliest Java Application Servers, and has stood the test of time due to engineering prowess.
The vulnerability is caused do to an improper sanitization of the 'file' parameter when used for reading help files. An attacker can exploit this vulnerability by directly requesting a '.jsp' file for example in the root directory of the server to view its source code that might reveal sensitive information.