Attack Technique 5: DCShadow Attack
DC Shadow Attack: Overview and Mitigation Strategies
Introduction
A DC Shadow attack is a highly sophisticated method of compromising an Active Directory (AD) environment. By introducing a rogue domain controller (DC) into the network, attackers can manipulate and replicate changes within the AD infrastructure, effectively taking control of critical directory services.
Attack Overview
Exploited Protocol: Kerberos Authentication (Windows Networks)
Targeted Account: Domain Administrator or similar privileged accounts
Primary Goal: Unauthorized modification and replication of AD objects for persistent control over the network.
Attack Steps
Create/Modify AD Objects: Attackers modify objects such as user accounts, groups, or permissions.
Replicate Changes to Legitimate DCs: Changes made by the rogue DC are replicated to other legitimate DCs.
Register SPNs for Rogue DC: The attacker registers Service Principal Names (SPNs) to the rogue DC for authentication.
Register Rogue DC in AD: The rogue DC is temporarily registered within the AD namespace.
Push Replication Data to Rogue DC: The rogue DC retrieves and replicates sensitive information.
Delete SPNs and Rogue DC: To cover tracks, the rogue DC and associated SPNs are deleted.
Impact
Persistence: Attackers gain long-term access to modify or create AD objects without detection.
Control: Changes made to AD are replicated across legitimate domain controllers.
Stealth: Deletion of rogue DCs and SPNs makes detection difficult.
Tools and Techniques for DC Shadow Attacks
Tool 1: Mimikatz
Mimikatz is a post-exploitation tool often used for credential dumping and ticket manipulation, including the DC Shadow attack.
Step 1: Elevating Privileges and Making Changes
Initialize Mimidrv Service: Gain SYSTEM privileges to operate as a rogue DC. Command:
Modify Target Object: Modify the SidHistory attribute of a user object (e.g., Alice). Command:
Step 2: Push Changes to Legitimate DCs
Push Replication Data: Register the rogue DC and push changes to legitimate DCs. Command:
Unregister Rogue DC: After modifications, unregister the rogue DC to avoid detection.
Detection Methods for DC Shadow Attacks
1. Network Monitoring
Monitor DRSUAPI Remote Procedure Calls (RPC), specifically the DRSUAPI_REPLICA_ADD operation. If requests originate from non-DC systems, it indicates a potential rogue DC.
2. Event Log Analysis
Key Windows Event IDs to monitor include:
Event ID 5136: Indicates changes to directory service objects. Key Fields:
Security ID,Account Name,Account Domain,Logon ID.Event ID 5141: Indicates the deletion of directory service objects. Key Fields:
Security ID,Account Name,Account Domain,Logon ID.
3. Active Directory Monitoring
Monitor changes to AD objects, including:
NTDSDSA objects: These represent the rogue DC.
SPN registrations: Look for unauthorized SPN registrations (e.g.,
GC/<host>).
Regular monitoring of these objects can reveal suspicious activities before they are removed.
Mitigation Techniques for DC Shadow Attacks
1. Implement Firewall Policies
Host-Based Firewalls: Limit lateral movement by restricting unauthorized network access.
Remote Protocol Restrictions: Allow RDP and other remote management protocols only from trusted sources.
2. Limit User Privileges
Minimize Privileged Accounts: Restrict the number of accounts with administrative privileges across security boundaries.
3. Control Access to Computer Objects
Restrict Object Creation: Limit permissions for creating new computer objects in AD to prevent unauthorized domain controllers.
4. Reduce Delegated Administrative Permissions
Privileged Group Governance: Ensure built-in groups (e.g., Domain Admins) are well-governed, and delegate permissions minimally.
5. Maintain Active Directory Hygiene
Clean Up Unused Objects: Regularly remove unused computer objects, sites, and NTDSDSA objects.
Audit SPN Changes: Regular audits of SPN registrations help identify rogue entries.
6. Leverage Monitoring Solutions
Use SIEM (Security Information and Event Management) solutions to aggregate and analyze logs for early detection.
Conclusion
A DC Shadow attack is a potent method of compromising an Active Directory environment, allowing attackers to persistently and stealthily control directory objects. By introducing a rogue domain controller, adversaries can replicate unauthorized changes to legitimate DCs, bypassing traditional detection mechanisms.
To defend against this advanced threat, organizations must adopt a multi-layered security approach that includes privilege management, network monitoring, and continuous auditing. By implementing robust mitigation techniques and maintaining strong AD hygiene, organizations can significantly reduce the risks associated with DC Shadow attacks and protect their critical infrastructure.
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