In Apache Struts 2.5 to 2.5.14, the REST Plugin is using an outdated JSON-lib library which is vulnerable and allow perform a DoS attack using malicious request with specially crafted JSON payload.
https://security.netapp.com/advisory/ntap-20171214-0001/
https://cwiki.apache.org/confluence/display/WW/S2-054
http://www.securitytracker.com/id/1039946
http://www.securityfocus.com/bid/102021
http://www.oracle.com/technetwork/security-advisory/cpujul2018-4258247.html
http://www.oracle.com/technetwork/security-advisory/cpuapr2018-3678067.html