The DCShadow attack is a stealthy and advanced technique used to manipulate Active Directory (AD) data by simulating a rogue domain controller. Here’s a breakdown of how it works and why it’s so dangerous:

🕵️‍♂️ What Is DCShadow?

DCShadow is a post-exploitation technique that allows an attacker to inject malicious changes into Active Directory by impersonating a domain controller. It was introduced via the Mimikatz tool and leverages legitimate replication protocols to avoid detection.

🧬 How the Attack Works

1. Admin Privileges Required:

   • The attacker must already have Domain Admin or Enterprise Admin rights.

2. Register a Rogue DC:

   • The attacker modifies the AD schema to make a workstation appear as a domain controller.
   • This involves creating new server and nTDSDSA objects in the Configuration partition.

3. Set SPNs (Service Principal Names):

   • These are needed for Kerberos authentication, allowing the rogue DC to communicate like a real one.

4. Push Malicious Changes:

   • The rogue DC replicates changes such as:
     • Adding users to privileged groups
     • Changing passwords
     • Modifying security descriptors

5. Trigger Replication:

   • The attacker forces replication so legitimate DCs accept and apply the changes.

6. Clean Up:

   • The rogue DC is removed to cover tracks, making detection extremely difficult.

🧨 Why It’s Dangerous

• Bypasses Logging: Changes are replicated using legitimate protocols, so they often evade SIEM and event logs.
• Persistence: Attackers can create backdoors or maintain access long-term.
• No Patch Available: It exploits valid replication features, not a vulnerability.

🛡️ How to Defend Against DCShadow

• Monitor AD Schema Changes: Use tools to detect unauthorized modifications in the Configuration partition.
• Audit Replication Events: Look for unusual replication activity (Event IDs 4928, 4929).
• Limit Admin Privileges: Apply least privilege principles and monitor privileged account usage.
• Use Directory Synchronization Monitoring: Track replication cookies and changes to directory state.

For a deeper dive, check out this detailed explanation from Netwrix or the MITRE ATT&CK entry on Rogue Domain Controller.