Apache Struts 2.0.0 through 2.3.24.1 does not properly cache method references when used with OGNL before 3.0.12, which allows remote attackers to cause a denial of service (block access to a web site) via unspecified vectors.
http://www.securitytracker.com/id/1036018
http://www.securityfocus.com/bid/90961