Scenario: DC Sync Attack Detected and Mitigated

April 2025

A DC Sync attack is a sophisticated Active Directory (AD) credential theft technique. An attacker with replication permissions requests hashed credentials for all users, including privileged accounts, from a domain controller (DC). If not detected early, this can lead to a complete domain compromise.

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1. Initial Threat Detection: Spotting Unusual Directory Replication Requests

Detection Sources:

• SIEM logs: Analyze logs from domain controllers for abnormal authentication and replication events.

• Network traffic analysis: Monitor communication between endpoints and DCs for suspicious patterns.

• Endpoint security agents: Detect malicious activity (e.g., unauthorized tools) on administrative machines.

• IAM Logs: Track permission changes and unauthorized requests in Active Directory.

Key Indicators of Attack:

1. A non-DC machine (e.g., a compromised endpoint) initiates unexpected replication requests.

2. Event IDs 4662 (Directory Access) and 4928 (Replication Requests) appear in logs from unknown or unauthorized sources.

3. Abnormally high retrieval of NTDS.dit credentials, which typically occurs only during legitimate DC replication.

4. Kerberos or NTLM requests originating from endpoints with no history of such activity.

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2. Data Collection & Correlation: Confirming the DC Sync Behavior

XDR aggregates and analyzes data from multiple sources:

• Active Directory Logs: Track abnormal access or excessive directory queries.

• Network Traffic Logs: Identify unusual Kerberos or NTLM activity and replication traffic.

• Host-Based Activity: Detect suspicious scripts or tools (e.g., Mimikatz) running on endpoints.

• Threat Intelligence: Correlate detected behaviors with known DC Sync attack patterns.

Advanced Detection:

• Using machine learning, XDR identifies that replication requests are coming from a non-DC system.

• Anomalies are flagged based on deviations from baseline behavior, such as unexpected access patterns or high replication volumes.

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3. Automated Response Actions: Mitigating the Attack

1. Immediate Isolation: The compromised machine is removed from the network to halt unauthorized replication.

2. Account Lockdown: The credentials used in the attack are disabled and flagged for review.

3. Firewall Blocking: Network policies are updated to block replication requests from unauthorized devices.

4. Alert Escalation: A high-priority alert is issued in the XDR console with full forensic details for further analysis.

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4. Investigation & Security Reinforcement

Steps:

• Analysts trace the origin of the replication requests, identifying the endpoint and credentials involved.

• They audit replication permissions and identify misconfigurations or privilege escalations that enabled the attack.

• Review logs for signs of lateral movement, such as additional compromised accounts or endpoints.

Mitigation & Hardening:

1. Restrict replication permissions to only legitimate domain controllers.

2. Implement tiered admin access, limiting exposure of privileged accounts.

3. Deploy monitoring solutions to detect unauthorized replication attempts in real-time.

4. Harden AD security policies, such as enforcing Kerberos encryption and auditing sensitive group memberships.

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Outcome

✅ DC Sync attack detected and blocked before critical damage. ✅ Unauthorized replication prevented, and privileged credentials protected. ✅ Compromised accounts and endpoints isolated to avoid lateral movement. ✅ Active Directory security posture improved based on forensic insights.

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