Apache Struts 2 before 2.3.14.2 allows remote attackers to execute arbitrary OGNL code via a crafted request that is not properly handled when using the includeParams attribute in the (1) URL or (2) A tag.
https://cwiki.apache.org/confluence/display/WW/S2-013
https://bugzilla.redhat.com/show_bug.cgi?id=967656