Friday, September 22, 2017

dbghost.exe - Ghost And The Darkness

I found another Device Guard bypass recently.  It was great to get to work with MSRC to get confirmation of the bypass, and to have them update the Device Guard configurations here:

Device Guard Configuration

This is another example of a misplaced trust bypass.  A trusted signed binary that can allow unapproved execution.

I'll keep this post short and sweet.

This tool is well documented on MSDN:

How to Use the Debug Diagnostic Tool v1.1 (DebugDiag) to Debug User Mode Processes

Read that carefully ;-)

So... dbghost will execute vbs scripts.  The next question is, what form? Anything special to do?

This is what caught my eye:

'Load the .NET debugger extension sos.dll (2.0 version)
CmdOutput = g_Debugger.Execute("!load C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\SOS.dll")
'Get the size of the GC
CmdOutput = g_Debugger.Execute("!eeheap -gc")

Couple of things there. If you are familiar with windbg, you will recognize that this allows you to not only execute .vbs... But you can execute windbg commands too.

Check out Matt Graeber's  example of some things you could do with windbg scripts:

Bypassing Application Whitelisting by using WinDbg/CDB as a Shellcode Runner

Thats it, I'll leave it for you to explore your own implementation here.

Special thanks to Matt Graeber  and Matt Nelson for the ideas, inspiration, and confirmation of the bypass.

This tool is not default, but it may be in your fleet.

Thats all for now. Reading MSDN pays off again ;-)



Sunday, September 17, 2017

Demogorgon - A Stranger Things Inspired Tool, Coming Soon.

This tool is inspired by the show "Stranger Things".
There are spoilers, so, if you want to watch the show, read no further.
You were warned.  :-)

First some background.  If you haven't seen the show.

In the show, an alternate reality, called the Upside Down is introduced.  Think of this as an overlay to the real world, same infrastructure and objects, but unseen, and inhabited with monsters.

"The Upside Down is an alternate reality or dimension existing in parallel to the human world. It contains the same locations and infrastructure as the human world, but it is much darker, colder, foggier..."

In one of the scenes, they discuss the Vale of Shadows from a D&D book...

"The Vale of Shadows is a dimension that is a dark reflection, or echo, of our world. It is a place of decay and death, a plane out of phase, a [place] with monsters. It is right next to you and you don’t even see it..."

Over the summer, I took some time off to reflect and think about things... While binge watching the show, I was inspired to think about Apex actors.  :-).  The result was a show inspired tool I wrote.

By Apex actors, I mean those actors that are untouchable so to speak.  Think of apex predators in the natural world.  These are the animals at the top of the food-chain...

Ok.  So the question becomes, if we are really into "Adversarial Emulation", how can we mimic the actions of these actors.  What exactly are Apex actors capable of?

Here would be a short list of what I would consider examples of Apex actor capabilities:

So, while we may think our Red Team operates like an Apex actor, we probably do not. 

So, what is the point of this post?

Over my time off this summer, I spent a fair amount of time exploring the idea of releasing a set of tools/capabilities to be able to emulate an Apex actor.

I wanted to build something that would give teams the ability to step up their game.  I want limited distribution to keep the "mystique" and to not to be a commodity tool.  

I wanted to something to allow Red Teams to operate from the "Upside Down" ;-).

The Upside Down being a Stranger Things reference to being able to operate from an "undetectable dimension", and interact with the actual infrastructure of an organization.  

Geeky? Yes. Possible? Absolutely.

I developed a tool, I'm calling Demogorgon:

"What’s a Demogorgon? Why were they so afraid to face it in battle? Demogorgon is none other than the Prince of Demons, and has been an iconic D&D creature since 1975, along with Orcus, his chief rival and enemy. You can find a short description of Demogorgon in the 5th edition Monster Manual under the Demon Lords section (pgs. 51-52), and a brief mention in the 5th edition Dungeon Master’s Guide in The Abyss section (pg. 62)." [1]

I will first share some of my architectural decisions and capabilities that I built into the tool.  The idea was to be a "rootkit-like thing".  Rootkits are interesting, in that they want to run, they want to hide. Some traditional rootkit capabilities just aren't always necessary, and will likely get you caught by modern Operating System defenses. 

Some things I've added include:
  • Novel execution, migration and repair capabilities. (The Flea)
  • Detailed logging and reporting from Red Team use.  
  • Modules delivered as keyed byte arrays.  Minimize PE structures, RWX regions etc... (Inspired by Ebowla )
Do we really need a new tool?  Maybe, if you don't think so, don't use it... Its not going to be for everyone anyway.  I wanted to learn some advanced tactics.  I wanted to push past modern detections and advance defender detection capabilities. 

I intend limited distribution to friends and family.  Once I've got the bugs worked out, I'll distribute to a wider audience, maybe.  I intend to limit distribution.  Maybe it will only be available west of the Mississippi :-) .

This tool is not meant to compete with tools like Empire, Cobalt Strike, or Metasploit.  From host based to network based, many organizations are prepared for and have strong detection capabilities for these tools.

These are all still highly effective tools, but they often have strong signatures and detections built around them.

If all goes well, the final development will be ready for October 31st release.  

Thats it, just a sneak peak of stranger things to come.

The idea behind Demogorgon, is to give Blue Teams a chance to face their nightmare, something they have never seen before, and something that they can't see.

Feel free to DM if you want to be added to the list of technical reviewers.



Saturday, September 2, 2017

Banned File Execution via InstallUtil.exe Nov 11, 2014 12:58 AM

I was going through some of my old research today, and thought I might share the genesis of one of my older findings.  I thought maybe it would be helpful to share my thinking and motivation for some of the research I have done in the past.

It was October 31, 2014.  We were running a Red Team exercise against our environment, it was the first engagement we had conducted since deploying our then Bit9 App whitelisting software.  Which was kicking our asses.  We had to learn to completely retool.  Dropping arbitrary unsigned, unapproved binaries was NOT going to work..

So, in an effort to try to circumvent the whitelisting we started enumerating all default .NET binaries on the system we were on.  We had proved earlier that year, this might actually be a useful angle for attack.  Details here: Application Whitelist Bypass Using IEExec .

For each binary, we asked the question.... How could I get this binary to execute my code... We were looking in:


The default path on Window 7.

After a couple hours trolling MSDN we worked our way alphabetically through the list of Assemblies.  We landed on InstallUtil.exe

InstallUtil.exe on MSDN

Now we needed to find a sample or understand HOW InstallUtil triggers execution... No real luck so we decided to Reverse the Assembly.

We used a .NET tool called ILSpy, you can also use dnSPy.

The first path from the args input passed to a Method call occurs on line 18.

This is important, cause we want to know what we can control or influence to get our assembly to execute.  We needed to know what InstallUtil.exe is looking for.  We can trace the arguments as they pass through ManagedInstallerClass.InstallHelper().

For sake of brevity...  We learned that we can influence InstallUtil.exe by crafting an Assembly that gets ingested by InstallUtil.exe and executed. If you continue to read/work through the Assembly. You will find that you need to decorate a class with the attribute

This lead to some really interesting behavior.  We discovered, we could execute this file in our environment,  EVEN if we explicitly banned that file.  This can be execute by any normal user and does not require any additional privileges to execute.

This was a real gem for sure.  We used the utility InstallUtil.exe to complete our mission and about a week and a half later, I finally had some time to report to the vendor. I posted a question to Bit9 in their User Exchange.

I won't share all the details of my original post, but the Carbon Black [CB] User Exchange is a fantastic way to share configuration data, Threat Intel and its a huge asset for CB customers and still is.

CB engineering immediately reached out to me and began digging into the internals of what caused this behavior, and it was subsequently fixed in later releases of their product.

Carbon Black (Bit9 when I was growing up ;-) . Has formal disclosure mechanism in place and they are really great to work with.  Reporting Security Vulnerabilities

So here we are almost 3 years since the original discovery of the use cases for InstallUtil.exe to bypass whitelisting deployments. At least original for me.  Others may have found but weren't blogging / talking about if they did....

If you want to test this against your environment, here is the original gist:

Shellcode via InstallUtil

Later we would write a full blown PE Loader for Mimikatz in InstallUtil

Mimikatz Inside InstallUtil

Here are some screen shots of my original dialogue / disclosure:

What does this all mean, and why am I posting this?

1. You should be aware of InstallUtil.exe as a mechanism to launch unapproved binaries.
2. When you find something, working with the vendor directly helps everyone be prepared.
3. Never stop being curious and investigating ways to adapt on an engagement.
4. InstallUtil has been seen in the wild example: Operation Cloud Hopper
5. This bypass, affects AppLocker as well as other Whitelisting tools.  Not Device Guard though.
6. .NET visibility is weak for a defender perspective, and its easy for an attacker to hide here.
7. App Whitelisting, even in audit mode allows you to track unsigned binaries as they move around your fleet.  For example, once we knew the hash, we could hunt where else it had landed.

I hope this was some helpful context on InstallUtil.exe and its history.

Feedback Welcome.



Friday, August 25, 2017

msxsl.exe Working As Designed.

So, I recently was exploring XSL, and injection and came across several interesting references.

<msxsl:script> Element

XSLT Script Block Sample

The basic gist, and what I think is interesting is that you can host/execute scripts inside trusted signed binaries that ingest XML.

So, here is an example, a tool called msxsl.exe.

You can download it here:

1. start /b msxsl.exe customers.xml report.xsl
2. start /b msxsl.exe report.xsl
3. start /b msxsl.exe customers.xml

The sample code above just show a very basic example.   If you look at the parameters accepted, either the xml or xsl file can be a url.

So, msxsl.exe while not default, may exist in your fleet, and it packs a powerful punch. It is a trusted binary that can be used to bypass some script controls.

Here again, you have a tool, that is working as designed, yet gives has functionality that can easily circumvent many controls.

By that I mean, execution events are likely not being noticed.... And it allows you to load and execute vbs/js and more...

I recently updated a sample you can use for testing.  So, I using the amazing DotNetToJscript, all you need is to update the base64 shell code here and you can execute in the context of msxsl.exe.  Keep in mind its a 32 bit application.

MSXSL Test Cases

You could easily base64 encode and deliver this script host runner too.  Its small but packs a big punch ;-)


Thats all.  Short and simple.


Casey Smith

Saturday, July 22, 2017

DEFCON 30 CFP: New Directions in Cryptanalysis, an Exploration of Disruptive Disclosure

I had some free time today, and started thinking about what would it be like to disclose a globally disruptive vulnerability. Where and how would you do that? I started thinking about what might this actually look like. So I chose the theme as a rogue cipher punk team that solves some critical equations. How would they get the word out. Safely? While I'm working out the details, this is my fictional write up of what that CFP looks like in 2022. I know its a bit different than my other blog posts. But hopefully highlights the dependency and brittleness we have if this were to ever occur. I don't think we can really imagine the scale of disruption.

So, here it is my 2022 DEFCON 30 CFP, a work of fiction. The setting is 5 years after a globally disruptive disclosure affecting cryptographic algorithms. This is the CFP submitted to DEFCON 30, in 2022 to outline the events that took place. The idea is less focused on the how it the equations were solved, and more on the "now what"... that they have been...How would you distill down what you needed to say in 90 minutes. What does the audience know, what have they lived through...

Here you go:

Title of Presentation: New Directions in Cryptanalysis, an Exploration of Disruptive Disclosure
Presentation Length: 80 minutes 10 Minutes Q&A
Presenters:  Mallory

Abstract:  Cryptography in the modern era was based on the assumption that certain mathematical problems are difficult to solve. These algorithms were said to be intractable. This talk explores how our team found a solution in polynomial-time to the Discrete Log Problem (DLP) and the Integer Factorization Problem (IFP). These two problems are closely related as you are now aware. What did we do when we found solutions to these problems? This talk will discuss the challenges our team faced in communicating our research. We will explore the mathematical primitives and assumptions that led to our solution. This talk will focus on the implications these solutions had on the global infrastructure.  We will also explain the background behind the Cipher Suite Resilience (CSR) standard, and how organizations can be better prepared for rapid cipher suite shifts. From signed Kernel Drivers to secure Authentication and Communication. The impact of this disclosure was far reaching. Hardly an area of modern technology was not affected by this disclosure. This talk will be a behind the scenes look at the events of 2017.  Including detailed information on how we disclosed the solution and remained anonymous. We think this talk will help organizations be better prepared for the next globally disruptive disclosure.

Bio: Mallory is a member of the Kult of Pythagoras (KoP), an international organization founded in 2005 with the idea that mathematical knowledge and solutions should no longer be held exclusively by any organization. These solutions and knowledge should be freely available for the benefit of humanity. The founding members are known only as Alice, Bob and Mallory.  In late 2017, Mallory revealed a solution to the Discrete Log Problem(DLP) and Integer Factorization Problem (IFP). Originally focused on internet security, their research has since had a direct impact on many fields including Genetics, Astronomy and many other Data-driven sciences. To this day the members of KoP remain anonymous.


1. Who is the Kult of Pythagoras? What do we believe, and what is our mission? (3-5 minutes)

A brief introduction about each of the founding members.  Our objectives and philosophy.

2. Talk Introduction.  Outline of what we will cover.  (10 minutes)

Modern mathematical research is shrouded in a language and mystique of its own. We will discuss the challenges we faced bringing forwarded a solution to the DLP & IFP. What are the realities faced by researchers wanting to disclose a globally disruptive solution?  Who did we tell first? How did we maintain equality for global disclosure? What means were used to alert authorities and organizations that a solution had been found.  What was adequate lead time to allow organizations to prepare for the disclosure?

3. Vintage Cipher Suite Background and primitives. (5 minutes)
It has now been proven these are solvable and cryptographic systems that use these should be decommissioned. This will lay the foundation for how these problems are related.

Discrete Log Problem (DLP)
Integer Factorization Problem (IFP)
Root Finding Problem (RFP)

4.  Roots of Unity - The Square Root of One. ( 15 minutes )
The solution to DLP and IFP resides in an elegant number, the square root of 1.  It was known that the square root with a prime modulus can be found efficiently using the Tonelli-Shanks Algorithm. By applying this to a composite modulus we were able to efficiently find factors of a modulus of any size. This also led to an alternative way to compute the multiplicative inverse of an exponent, the basis for many cryptographic schemes.
5.  The Disclosure - How we did it. Safely. (20 Minutes )
Solving these problems was only the beginning. Disclosing the solution to these problems is not often considered when working on a solution. The impact of solving these equations is of immense interest to certain individuals and organizations. In order to ensure that these solutions were not suppressed, we devised a scheme to announce to the world that we indeed had access to such solutions and were prepared to disclose them, for free. In order to better prepare the global community for our disclosure, Mallory devised a scheme for both proving to the world that we had a solution, and at the same time, protecting that solution until organizations were prepared. This is now known anecdotally as the "Your Crypto Has No Clothes" memo of December 2017. This led to a global effort to remove vulnerable cipher suites. While many organizations were caught unprepared, we feel that the gap between the memo and disclosure, allowed competent organizations to be understand what was on the horizon and to prepare.

6.  The Chase - How we were hunted. How we stayed safe. (10 Minutes )
Once we announced our intent to disclose, an organized effort took place to suppress the disclosure. By taking the proper countermeasures we were able to watch this unfold, and were alerted to encroachments on our privacy perimeter. Needless to say, there are people who did not want this solution to be disclosed. We quickly learned who was interested in suppressing this disclosure, and took steps to ensure the world got the solutions to these equations. We seek to inform future researchers of our lessons learned, and provide tips for future disruptive disclosure.

7. Cipher Suite Resilience (CSR) - Be ready for the next one. ( 10 Minutes )
In 2017 we learned how dependent our systems and protocols were in antiquated algorithms quickly. The disclosure revealed how critical, brittle and fragile our systems are and incapable of change. From this emerged the CSR, a suite of standards to prepare organizations, systems, and protocols for disruptive disclosures. We hope organizations are now adopting and implementing the recommendations in this standard.

8.  The Conclusion.  (5 Minutes )
We will close with our thoughts on the current events we see unfolding today.  The consequences of the lack of cipher resiliency, and ideas on how to move forward.

List of Conferences:  We have not presented this material to any other conferences.

Why is this a good fit for DEFCON:

We have been in attendance and participated in DEFCON for several years. We feel that our conversations and philosophies were heavily influenced by this community. We feel this is the best venue to bring forward the behind the scenes look at what happened in 2017. The responsible disclosure of these disruptive solutions proved to be much more difficult than we imagined. We hope to share our lessons learned so that other researchers can benefit.  We hope to inspire others to bring forward solutions that have been locked away.

Previous experience:
We have presented under different names at DEFCON, BlackHat, DerbyCon, multiple BSides events. We will present our original document of solutions for archive in the DEFCON proceedings.  

List of facilities requested: Mallory will provided a link to the video file securely to the organizers of DEFCON. This talk has been pre-recorded. In an effort to maintain our privacy, we hope you will accept this unusual talk delivery.

Monday, June 12, 2017

Attacking the CLR - AppDomainManager Injection

I have been interested in attacking CLR to be able to manipulate .NET apps, like PowerShell.
For example using .NET profilers here:

Recently I was reading this article about the CLR and execution events:

One of the interesting things I stumbled on was this reference to CLR tuning:

Of particular interest I saw these environment variables that can be set. You can also set these in an app.config file.

AppDomain Managers are interesting in that they setup the environment, before your .NET app runs.

I'll keep this short.  You can manipulate the runtime, by getting your code to execute prior to the application.

Here's some code.

This also can work against PowerShell.exe too.  ;-)

I leave it to you to explore whats possible here.

Have fun, keep asking questions!



Thursday, May 18, 2017

Subvert CLR Process Listing With .NET Profilers

I recently stumbled onto an interesting capability of the CLR.

"A profiler is a tool that monitors the execution of another application. A common language runtime (CLR) profiler is a dynamic link library (DLL) that consists of functions that receive messages from, and send messages to, the CLR by using the profiling API. The profiler DLL is loaded by the CLR at run time."

So. whats the big deal, really?

Turns out in .NET 4 allows for Registry-Free Profiler Startup and Attach.  This can lead to some unintended consequences.

In order for this work, you need to set 3 environment variables.

Again from MSDN:

Startup-Load Profilers

A startup-load profiler is loaded when the application to be profiled starts. The profiler is registered through the value of the following environment variable:
Starting with the .NET Framework 4, you use either the COR_PROFILER or the COR_PROFILER_PATH environment variable to specify the location of the profiler. (Only COR_PROFILER is available in earlier versions of the .NET Framework.)
  • COR_PROFILER={CLSID of profiler}
  • COR_PROFILER_PATH=full path of the profiler DLL
If COR_PROFILER_PATH is not present, the common language runtime (CLR) uses the CLSID from COR_PROFILER to locate the profiler in the HKEY_CLASSES_ROOT of the registry. If COR_PROFILER_PATH is present, the CLR uses its value to locate the profiler and skips registry lookup. (However, you still have to set COR_PROFILER, as discussed in the following list of rules.)
So, if our objective is to hijack a .NET process, like say PowerShell, we don't really want a Profiler to load, we just want to be able to manipulate the process.  It turns out you can get a dll to load into the .NET process that is not even a Profiler.  This was interesting to me.  The CLSID is just random for this purpose.

So, I had this idea, I could write quick POC DLL that hides a process from PowerShell.  Well, short story is this.  If you load a Profiler, and don't properly setup the Profiler structures, then the .NET CLR will promptly eject your dll.

For details of how we hook and hide see this article.

Thats ok.  ;-)  So what I did was create a DLL that loads another DLL from memory, and then when my profiler gets evicted, my hooking dll will stay resident.  So the Profiler just becomes a bootstrap.

The result seen in this clip below.  We enumerate processes with Get-Process in a "non-profiled" PowerShell process.  We get the details just fine.  Then we set our environment variables, load our PowerShell process, and now, the processes are not seen.


Why does this matter.  As PowerShell become the window through which many sysadmins poll and interrogate the operating system.  By using attaching a malicious profiler, we can mold the output so to speak to be what we want.

This was just a very basic example.  I leave it up to you to explore further capabilities of tampering with the CLR/.NET applications through profilers.

Hope that was helpful.

Thats all for today.