CVE Number:         CVE-2013-2248
Title:              Struts2 Prefixed Parameters Open Redirect Vulnerability
Affected Software:  Apache Struts v2.0.0 - 2.3.15
Credit:             Takeshi Terada of Mitsui Bussan Secure Directions, Inc.
Issue Status:       v2.3.15.1 was released which fixes this vulnerability
Issue ID by Vender: S2-017

Overview:
  Struts2 is an open-source web application framework for Java.
  Struts2 (v2.0.0 - 2.3.15) is vulnerable to open redirect (and possibly
  HTTP response header injection). This is caused by insecure design of
  prefixed parameters (redirect: and redirectAction:)
  in DefaultActionMapper class of Struts2.

Details:
  Struts2's ActionMapper is a mechanism for mapping between incoming HTTP
  request and action to be executed on the server. DefaultActionMapper is
  a default implementation of ActionMapper. It handles four types of
  prefixed parameters: action:, redirect:, redirectAction: and method:.

  Among these four prefixed parameters, redirect: and redirectAction: can
  be used for open redirect attacks.

  For example, redirect prefix is used for HTTP redirect.

  Normal redirect prefix usage in JSP:
    <s:form action="foo">
      ...
      <s:submit value="Register"/>
      <s:submit name="redirect:http://www.google.com/" value="Cancel"/>
    </s:form>

  If the cancel button is clicked, redirection is performed.

  Request URI for redirection:
    /foo.action?redirect:http://www.google.com/

  Resopnse Header:
    HTTP/1.1 302 Found
    Location: http://www.google.com/

  Usage of redirectAction: is similar to redirect.
  See Struts2 document for details.
  https://cwiki.apache.org/confluence/display/WW/ActionMapper

  The problem is that applications cannot restrict destination URL of
  redirect. Furthermore, prefixed parameters are quite forceful. It means
  that behavior of application which is not intended to accept prefixed
  parameters can also be overwritten by prefixed parameters added to HTTP
  request.

  Therefore any struts2 application that use DefaultActionMapper can be
  open redirector simply by adding redirect: / redirectAction: prefixed
  parameters.

  The last thing that should be mentioned is that Struts2 passes redirect
  URL to ServletHttpResponse#sendRedirect() even if the URL contains line
  breaks. Impact of this behavior depends on the container server that
  hosts Struts2.

  As far as I know, recent versions of Tomcat filters line breaks, but a
  few servers such as WebLogic do not filter line breaks (More precisely,
  WebLogic blocks CR+LF sequence but you can bypass it in several ways).
  In such server environment, the behavior of Struts2 apparently causes
  HTTP response header injection.

Proof of Concept:
  PoC is already disclosed on vender's web page.
  https://struts.apache.org/release/2.3.x/docs/s2-017.html

  Below PoC URLs are just quotes from the vender's page.
  http://host/struts2-showcase/fileupload/upload.action?redirect:http://www.yahoo.com/
  http://host/struts2-showcase/modelDriven/modelDriven.action?redirectAction:http://www.google.com/%23

  HTTP response header injection PoC.
  http://host/struts2-blank/example/HelloWorld.action?redirect:x%0ASet-Cookie:x%3D123
  http://host/struts2-blank/example/HelloWorld.action?redirect:x%0DSet-Cookie:x%3D123
  http://host/struts2-blank/example/HelloWorld.action?redirect:x%0D%0A+Set-Cookie:x%3D123
  (These URLs work on specific servers and specific browsers only)

Timeline:
  2013/06/26  Reported to Struts Security ML
  2013/07/17  Vender announced v2.3.15.1
  2013/08/10  Disclosure of this advisory

Recommendation:
  Upgrade to the latest version. As stated in the vender's page,
  redirect: and redirectAction: parameters were completely dropped and
  do not work in the latest version. Thus attention for compatibility
  issues is required for upgrade.

Reference:
  https://struts.apache.org/release/2.3.x/docs/s2-017.html
  https://cwiki.apache.org/confluence/display/WW/ActionMapper