In Struts 2 before 2.3.15.1 the information following “action:”, “redirect:”, or “redirectAction:” is not properly sanitized and will be evaluated as an OGNL expression against the value stack. This introduces the possibility to inject server side code.
View the template here CVE-2013-2251.yaml
References:
http://cxsecurity.com/issue/WLB-2014010087