In Apache Struts 2.5 to 2.5.14, the REST Plugin is using an outdated JSON-lib library which is vulnerable and allow perform a DoS attack using malicious request with specially crafted JSON payload.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://github.com/advisories/GHSA-xcrm-qpp8-hcw4
https://euvd.enisa.europa.eu/vulnerability/EUVD-2018-0714
https://cwiki.apache.org/confluence/display/WW/S2-054
http://www.oracle.com/technetwork/security-advisory/cpujul2018-4258247.html
http://www.oracle.com/technetwork/security-advisory/cpuapr2018-3678067.html