Exploiting WDAC: How Attackers Bypass EDR Sensors and What to Do

In the ever-evolving chess game of cybersecurity versus threat actors, a new, insidious tactic has emerged. This latest exploit weaponizes Windows Defender Application Control (WDAC) to effectively bypass Endpoint Detection and Response (EDR) sensors, leaving organizations vulnerable to highly dangerous and stealthy attacks. Let’s unpack how this attack works and, more importantly, what you can do to mitigate it.

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What Exactly is Happening?​

Among the arsenal of tools that IT administrators can employ, Windows Defender Application Control (WDAC) plays a vital role. Introduced with Windows 10 and Windows Server 2016, WDAC is a feature designed to offer granular administrative control over what code can or cannot execute within a Windows environment. Think of it as the gatekeeper that ensures only trusted applications get to play within your digital ecosystem.
However, bad actors have turned this gatekeeper into an accomplice through a sophisticated and chillingly smart exploit. Leveraging WDAC’s legitimate features, these attackers are using custom WDAC policies to disable EDR processes—those essential watchdogs designed to detect malicious activity on your systems.
The method, categorized under the MITRE ATT&CK framework as part of the "Impair Defenses" tactic (Technique ID: T1562), is particularly pernicious because it uses administrative privileges to rewrite the rulebook. By crafting rogue WDAC policies, attackers can systematically block EDR software from running at startup. Picture a fortress where the intruders not only snuck in but also dismantled the alarm system and locked it in silence—the house is wide open.

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How Does the Attack Work? A Step-by-Step Breakdown​

The attack unfolds across three distinct phases, each employing legitimate functionality in a subversive way:

1. Policy Creation and Placement​

The attacker creates a specially tailored WDAC policy file. This file includes permissions to execute their own tools while actively blocking critical security software, including the all-essential EDR sensors. They plant this malicious policy in the C:\Windows\System32\CodeIntegrity directory on the target system. This is where WDAC policies reside and take effect.

2. System Reboot​

Here’s the kicker—WDAC policies are only enforced after a reboot. Once the attacker plants their wicked little policy, all they need is a simple system restart. After booting back up, the malicious WDAC policy takes center stage and controls what processes are allowed to run (or not run).

3. EDR Shutdown​

When the system boots back up, the malicious policy prevents EDR tools from loading. This effectively blinds the system, giving attackers free rein to run undetected. What’s worse? Tools like this do not create the immediate and noisy chaos that ransomware attacks typically do—making the whole operation dangerously silent.

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A New Tool for Sleepless Administrators: The Krueger Proof-of-Concept​

In an unsettling development, a legitimate proof-of-concept (PoC) tool known as Krueger has surfaced. Created by security researcher Logan Goins, Krueger is a double-edged sword. While on one hand such tools often serve to demonstrate vulnerabilities and help improve defenses, in the wrong hands, they become optimized weapons for exploitation.
Krueger operates directly in system memory as part of post-exploitation activities, enabling attackers to deploy it covertly without leaving much of a trail. Essentially, once attackers gain administrative access to a machine, Krueger amplifies their ability to render EDR ineffective.

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Why is This a Big Deal?​

The impact of this attack vector isn’t confined to individual machines. If an attacker secures domain admin privileges, they can propagate this exploit across an entire organization's IT infrastructure—outmatching endpoint defenses at scale. Hypothetically, in environments with hundreds or thousands of devices, this could completely nerf an organization’s cybersecurity defenses in one fell swoop.

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Mitigation Strategies: Fight Back​

As alarming as this attack is, solutions do exist. Here’s how your organization can fortify itself against this threat:

1. Enforce WDAC Policies Centrally​

• Use Group Policy Objects (GPOs) to deploy network-wide WDAC policies that override any local, rogue tampering.
• By centralizing control, you block attackers from distributing unauthorized policies to individual endpoints.

2. Principle of Least Privilege​

• Restrict administrative privileges across your network. Limit which users or accounts have access to modify WDAC policies or access sensitive system folders like C:\Windows\System32\CodeIntegrity.

3. Harden Administrative Controls​

• Lock Down Local Admin Accounts: Tools like Microsoft’s Local Administrator Password Solution (LAPS) can help manage local administrator account credentials securely and limit exposure.
• Restrict access to sensitive directories and SMB shares, leaving fewer avenues for attackers to inject malicious policies.

4. Regular Audits and Monitoring​

• Conduct regular audits of running WDAC policies across your fleet of endpoints. Uncover any unexpected or unauthorized modifications immediately.
• Leverage SIEM (Security Information and Event Management) systems to identify anomalies, such as sudden policy file modifications or unexplained system reboots.

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The Bigger Picture​

This latest attack serves as yet another reminder of the cat-and-mouse game between defenders and cybercriminals. What makes it particularly unsettling is how it repurposes a tool built to enhance security into one that undermines it.
But this underscores the necessity of a layered defense strategy. Relying solely on endpoint security tools like EDR is no longer sufficient in today’s cyber landscape. Organizations must adopt a holistic approach, combining rigorous system monitoring, administrative best practices, and user education to stay one step ahead of the attackers.

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Final Thoughts​

As Mark Johnson, CISO of a Fortune 500 company, aptly put it: “Organizations need to be aware of this threat and take proactive measures. Implementing strong access controls and regularly auditing WDAC policies are now more crucial than ever.”
The key takeaway? Cybersecurity is not a one-time setup—it's a continuous process of assessment, adaptation, and improvement. Whether you’re a seasoned IT admin or a small business owner learning the ropes, vigilance and proactivity are your most potent weapons. After all, every gatekeeper needs someone watching their back.
Got questions or thoughts about this article? Join the discussion on WindowsForum.com! This is your community—let's talk about how to keep Windows safe and secure.

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Source: Cyber Security News New Sophisticated Attack Weaponizes Windows Defender to Bypass EDR