Apache Struts 2.3.19 to 2.3.20.2, 2.3.21 to 2.3.24.1, and 2.3.25 to 2.3.28, when Dynamic Method Invocation is enabled, allow remote attackers to execute arbitrary code via method: prefix, related to chained expressions.
https://www.exploit-db.com/exploits/39756/
https://struts.apache.org/docs/s2-032.html
http://www.securitytracker.com/id/1035665
http://www.securityfocus.com/bid/91787
http://www.securityfocus.com/bid/87327
http://www.oracle.com/technetwork/security-advisory/cpuoct2016-2881722.html
http://www.oracle.com/technetwork/security-advisory/cpujul2016-2881720.html
http://www.huawei.com/en/psirt/security-advisories/huawei-sa-20160527-01-struts2-en