Apache Struts 2.0.0 through 2.3.x before 2.3.20 uses predictable <s:token/> values, which allows remote attackers to bypass the CSRF protection mechanism.
http://www.securitytracker.com/id/1031309
http://www.securityfocus.com/bid/71548
http://www.securityfocus.com/archive/1/534175/100/0/threaded
http://www.oracle.com/technetwork/topics/security/cpujul2015-2367936.html
http://www.oracle.com/technetwork/topics/security/cpuapr2015-2365600.html
http://www.oracle.com/technetwork/security-advisory/cpuoct2016-2881722.html
http://struts.apache.org/docs/s2-023.html
http://packetstormsecurity.com/files/129421/Apache-Struts-2.3.20-Security-Fixes.html