The DCSync attack is a powerful post-exploitation technique that allows an attacker to simulate a domain controller and extract sensitive data from Active Directory, including password hashes. Here’s a detailed breakdown:

🧠 What Is a DCSync Attack?

DCSync is an attack that abuses the Directory Replication Service Remote Protocol (MS-DRSR) to request replication of user credentials from a domain controller. It’s a feature of tools like Mimikatz, Impacket, and DSInternals, and is often used to dump password hashes for accounts like krbtgt, which can be used to forge Golden Tickets.

🔍 How the Attack Works

1. Privilege Escalation:

   • The attacker must have an account with Replicating Directory Changes permissions—typically Domain Admin, Enterprise Admin, or delegated service accounts.

2. Simulate a Domain Controller:

   • Using tools, the attacker pretends to be a DC and sends replication requests.

3. Request Replication:

   • The attacker uses the GetNCChanges function to ask for user data.

4. Receive Sensitive Data:

   • The domain controller responds with password hashes, including NTLM and Kerberos credentials.

5. Use Extracted Hashes:

   • These can be cracked offline or used in attacks like Pass-the-Hash, Golden Ticket, or Silver Ticket.

🎯 Why It’s Dangerous

• No need for DC access: Can be executed remotely.
• Stealthy: Uses legitimate replication protocols.
• Complete credential dump: Can target specific users or the entire domain.

🛡️ How to Defend Against DCSync

• Audit privileged accounts: Limit who has replication rights.
• Monitor replication traffic: Look for replication requests from non-DC machines.
• Use detection tools: Solutions like Netwrix Threat Manager can identify DCSync patterns.
• Implement tiered admin models: Separate high-privilege accounts from everyday use.
• Log and alert on suspicious behavior: Watch for Event IDs like 4662 (object access) and 4928/4929 (replication).

📚 Learn More

• Netwrix: What Is DCSync Attack?
• Lepide: DCSync Attack and Protection
• Altered Security: Primer on DCSync