Insights and Research

Deception Engineering

Disrupting attempts to exploit GPP Saved Passwords

Deception Engineering

Introduction

One skill that the Zscaler Deception team has become really good at is analyzing adversary tactics, techniques, and toolsets and hypothesizing how we could disrupt the adversary playbook with deception. 

What we want to talk about today is a concept we like to internally call “Deception Engineering”. 

It’s a wordplay on Detection Engineering. In addition to focusing on writing rules to detect a specific type of technique or threat, security teams can also focus on how to deceive a technique or threat. We see it as an important component of Detection Engineering. 

 

What is Deception Engineering?

Deception Engineering is the process of building, testing, and implementing deception-based defenses within the enterprise to disrupt adversary operations and playbooks. 

 

Why Deception Engineering

Deception engineering broadens the scope of detection engineering to FORCE adversary behavior in addition to detecting threat behavior. 

 

The fundamental idea here is for defenders to use their knowledge and control of the environment they are defending and use it to their advantage to guide adversary choices within their environment. 

 

One of the main advantages of the deception approach is its simplicity. Thinking about deception use cases is simple because the underlying concept of “decoys” or “fakes” is also extremely simple. 

Here are a couple of examples:

  • Instead of writing password guessing detection rules that rely on thresholds and time-based analysis, simply set up a decoy account and monitor it for failed attempts. 
  • Instead of trying to detect SMB port scanning by writing rules on port access and baselines that are prone to false positives, set up a decoy system with SMB open and monitor it for connections. 

If defenders are able to control the motivation of the adversary and control the choices they make in an environment, the resulting telemetry is:

  • High Fidelity - the event can occur only under a malicious circumstance. 
  • Low False Positive - the event is highly unlikely to be carried out by regular software or user behavior. 
  • Controlled False Negatives - events that do not interact with deception are not captured and ergo cannot be missed

 

The Deception Engineering Process

The deception engineering process is actually quite simple to adopt. 

Broadly, here's what it looks like: 

  • Pick a business-aligned use case or a tactic / technique 
  • Describe the attack story by breaking down the steps of the  attack
  • Analyse the attack story for opportunities for implementing deception
  • Understand the telemetry you can get by implementing the deception opportunity
  • Implement the opportunities that work best in production 

We’ve described the process in detail below. 

 

Steps

Description

Tool / Technique / Tactic / Use Case

The description of the tool/technique/tactic you wish to deception engineer. For broader use cases, like “Ransomware Detection”, you may need to iterate over this process multiple times. 

Attack Tools

List all attack tools that can execute a technique or tactic

Attack Story

Describe the steps of the attack as if executed manually

Deception Opportunities

Hypothesize Deception Opportunities against attack steps

Realism Requirements

Identify parameters that must be configured to ensure your deception opportunities mimic real implementations

OpSec Safety Considerations

Call out any opsec safety considerations as not all deception opportunities are opsec safe.

Production Readiness

Choose techniques viable in production with due consideration to operational challenges

Telemetry

What telemetry can you gather if an adversary acts on deception

Detection Order**

Is this a first or second-order detection?

Test Results

Test cases and their efficacy. 

**Detection Order

First-order Detection- When an adversary interacts with a deceptive component that directly generates alert telemetry. 

Second-order Detection - When an adversary acts on deceptive information that leads them to a deceptive component that generates telemetry. 

Our approach is to create a specification that addresses each of these steps before we take the step of rolling out defenses to production.

 

Deception Engineering Group Policy Preferences Saved Passwords

Let’s apply the deception engineering process with an example.

For brevity, we have excluded a few steps in the process, but each step is an important consideration and must be documented when planning your deception approach. 

Review the MITRE ATT&CK mapped technique details here for Group Policy Preferences Saved Password (GPP)

Let’s begin!

 

About the attack

The GPP Saved Passwords issue has been around for close to a decade. The feature allowed Active Directory administrators to manage local administrator passwords via Group Policy. 

However, the policy configuration XML file that maintained the details of the policy, stored the password to the local administrator account encrypted in the file. With a decryption key made available, any domain user regardless of privilege could simply search for the file, decrypt the password and gain administrator access to all the machines to which the policy applied. 

We know for a fact now, that the Conti ransomware group had GPP password extraction as part of their technique arsenal as revealed in their playbook. Here's a screenshot from the playbook. 

 

 

Many organizations have already addressed this problem. But from a deception engineering lens, this is a missed detection opportunity.

 

If a Conti Ransomware affiliate was to target an organization, can we deceive them when they execute this tactic? Can we fool them into believing that they have access to legitimate credentials via GPP? Can we divert their attention as they execute their playbook and capture telemetry about their presence? And what telemetry can we give the defender so that they are able to act quickly to stop the threat? 

 

Let’s find out. 

 

STEP 1 - Layout the framework

We want to deception engineer a specific technique, in this case GPP, so we have built out a minimalist representation of specific steps we need to address for implementing our solution. 

 

 

STEP 2 - Explore tools used to exploit GPP

The next step in this process is to identify tools used to exploit this technique. The idea is to study and document how these tools works under the hood so we can abstract the attack flow to build an attack story.  This is especially important if we want to build tool-agnostic deception use cases. 

Here we have included two tools, get-gpppassword.ps1 and get-decrypt.py. 

 

 

STEP 3 - Describe the attack flow

Once we have understood how these tools work, we should be able to extract the attack story. Take a look at how we have abstracted the attack. Essentially:

  • Figure out how to search Groups.XML files and extract the credentials from it on a Domain Controller (DC)
  • Figure out where the discovered password is applicable
  • Test if you actually log in with the credentials. 

 

 

STEP 4 - Identify deception opportunities

Now that you have the story in place, add connections to possible deception opportunities. This step requires some creative thinking. 

Essentially you can:

  • Create a decoy OU
  • Join decoy machines to AD and move them to this decoy OU
  • Apply a GPP GPO to this OU

 

 

STEP 5 - Document possible telemetry you can gather for detection

Now, what telemetry can you actually get if you were to implement these deception opportunities? 

Because of the way Group Policy works, it may be very difficult to reliably distinguish between malicious and regular activity when it comes to access to the decoy Groups.XML. But it’s still valuable because we can use this setup as a Lure. 

Think of lures as pointers that tell the adversary “Hey here’s some interesting credentials and where you can apply it. Why don’t you go try a login?” 

This results in what we call a “second-order detection”. Our deceptive setup doesn’t generate telemetry unless the adversary acts on the information we have planted in AD. 

 

So the idea is if you see a login attempt against decoy systems you have setup using the credentials you have configured in the Groups.XML file, there’s only one way that could have happened. 

Someone is exploiting GPP. 

 

 

 

STEP 6 - Test your deception setup

The last step of this process is to test your deception setup. Use the tools you documented in the previous steps. 

  • Does your decoy setup show up in the output of these tools?
  • If you compare and contrast it with a “real” setup, is it indistinguishable?
  • Are there any considerations that might tamper with your setup in production? 

 

 

Closing Notes

Deception Engineering empowers defenders to control adversary choices in their network. 

It provides defenders with options, where the existing approaches might be overwhelming, complex, and prone to false positives, for an alternative that’s easier to understand, lower on false positives, and really fun to set up and implement. 

Do you want to brainstorm a deception engineering use case? 

Write to me!

 

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