The Apache Struts REST Plugin is using XStream library which is vulnerable and allow perform a DoS attack when using a malicious request with specially crafted XML payload. Upgrade to the Apache Struts version 2.5.16 and switch to an optional Jackson XML handler as described here http://struts.apache.org/plugins/rest/#custom-contenttypehandlers. Another option is to implement a custom XML handler based on the Jackson XML handler from the Apache Struts 2.5.16.
www.oracle.com/technetwork/security-advisory/cpujul2018-4258247.html
www.securityfocus.com/bid/103516
www.securitytracker.com/id/1040575
cwiki.apache.org/confluence/display/WW/S2-056
lists.apache.org/thread.html/r02c2d634fa74209d941c90f9a4cd36a6f12366ca65f9b90446ff2de3%40%3Cissues.struts.apache.org%3E
lists.apache.org/thread.html/rf482c101a88445d73cc2e89dbf7f16ae00a4aa79a544a1e72b2326db%40%3Cissues.struts.apache.org%3E
security.netapp.com/advisory/ntap-20180330-0001/