Apache Struts contains a Remote Code Execution when using results with no namespace and it's upper actions have no or wildcard namespace. The same flaw exists when using a url tag with no value, action set, and it's upper actions have no or wildcard namespace.
Apache Struts 2.0.0 through 2.3.15 allows remote attackers to execute arbitrary OGNL expressions via a parameter with a crafted (1) action:, (2) redirect:, or (3) redirectAction: prefix.