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Summary

Problem

The Struts 2 DefaultActionMapper used to support a method for short-circuit navigation state changes by prefixing parameters with "action:". This mechanism was action mapping mechanism supports the special parameter prefix action: which is intended to help with attaching navigational information to buttons within forms.

In Struts 2 before 2.3.15.2 the information following "action:" can easily be manipulated to access restricted content of actions in the same package.

Proof of concept

Modify web.xml in the Struts Blank app as follow:

...

    <security-constraint>
        <web-resource-collection>
            <web-resource-name>HelloWorld</web-resource-name>
            <url-pattern>/example/HelloWorld.action</url-pattern>
        </web-resource-collection>
        <auth-constraint>
            <role-name>admin</role-name>
        </auth-constraint>
    </security-constraint>
    
    <security-role>
        <role-name>admin</role-name>
    </security-role>

3, under certain conditions this can be used to bypass security constraints. More details will available later on when the patch will be widely adopted.

Solution

In Struts 2.3.15.3 the action mapping mechanism was changed to avoid circumventing security constraints. Two additional constants were introduced to steer behaviour of DefaultActionMapper:

• struts.mapper.action.prefix.enabled - when set to false support for "action:" prefix is disabled, set to false by default
• struts.mapper.action.prefix.crossNamespaces - when set to false, actions defined with "action:" prefix must be in the same namespace as current action

Thus adds a security constraint on action HelloWorld.action - try to open it directly and you will get Permission Denied error. To obey that use the below url:

http://host/struts2-blank/example/Login.action?action:HelloWorld

Solution

DefaultActionMapper was changed to forward request to the requested action by "action:" prefix - thus means instead of just updating current ActionMapping, the DefaultActionMapper creates a new result - ServletDispatchResult - and executes it.

...