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Vulnerability of dynamic method invocation
------------------------------------------

                 Key: WW-3264
                 URL: https://issues.apache.org/struts/browse/WW-3264
             Project: Struts 2
          Issue Type: Bug
    Affects Versions: 2.1.8
            Reporter: Alex Siman
            Priority: Critical


Dynamic method invocation is the security hole. If some of action methods has "public" visibility
and return String, then attacker can call this method. In the example below, attacker can
call method "changeAdminPassword()" of TestAction from URL like:
http://example.com/test!changeAdminPassword.action

public class TestAction
{
	private String currentPassword = null;

	@SkipValidation
	public String execute() throws Exception
	{
		if (getValidCurrentPassword().equals(currentPassword))
		{
			String feedback = changeAdminPassword();
			addActionMessage(feedback);
			return SUCCESS;
		}
		else
		{
			addFieldError("currentPassword", "Invalid password.");
			return INPUT;
		}
	}

	// Note "public" visibility here.
	public String changeAdminPassword()
	{
		String newPassword = "new-admin";
		// Persist changes here...
		return "Admin password has been changed to '" + newPassword + "'.";
	}
	
	public String getCurrentPassword()
	{
		return currentPassword;
	}

	public void setCurrentPassword(String currentPassword)
	{
		this.currentPassword = currentPassword;
	}
}


To fix this vulnerability we must leverage the [com.opensymphony.xwork2.config.entities.ActionConfig.allowedMethods].
And to prevent backward incompatibility, add new default setting like:

default.properties
==================
## Note "false".
struts.enable.DynamicMethodInvocation.restrictToAllowedMethods = false


Desired code in struts.xml
==========================
<package name="testPackage">
	<action name="login" class="actions.LoginAction">
		<result>/login.jsp</result>
		<allowedMethods>
			<allowedMethod>doLogin</allowedMethod>
		</allowedMethods>
	</action>

	<allowedMethods class="actions.LoginAction">
		<allowedMethod>doLogin</allowedMethod>
		<allowedMethod>doRegister</allowedMethod>
	</allowedMethods>

	<!— Or use <method>? -->
	<allowedMethods class="actions.UserAction">
		<method>create</method>
		<method>list</method>
		<method>view</method>
		<!-- ... -->
	</allowedMethods>
</package>


Desired code w/ Convention plugin:
(Note @AllowedMethod anno)
==================================
class LoginAction 
{
	@SkipValidation
	public String execute()
	{
		// Nothing.
		return INPUT;
	}

	@AllowedMethod
	public String doLogin()
	{
		// Method's body here...
		// password = getPasswordHash();
		return SUCCESS;
	}

	// This method cannot be invoked dynamically.
	public String getPasswordHash()
	{
		// Method's body here...
		return "xxx";
	}
}


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