First Time Seen Account Performing DCSync

The DCSync attack is a technique used to retrieve credential information from Active Directory, potentially leading to complete domain compromise. This attack involves initiating the Active Directory replication process, which is normally reserved for domain controllers. This detection identifies user accounts initiating this process for the first time, which can be an indicator of malicious activity. This activity is detected via Windows Security Event Logs and focuses on the identification of the initial use of replication protocols. Attackers exploit this to steal credentials or sensitive data stored within the Active Directory. This technique can be used to escalate privileges and move laterally within the network, eventually leading to data exfiltration or other malicious objectives.

Attack Chain

1. An attacker gains initial access to a system within the target network.
2. The attacker escalates privileges to obtain the necessary rights to perform DCSync. This may involve exploiting vulnerabilities or using stolen credentials.
3. The attacker uses a tool like Mimikatz or custom scripts to initiate the Active Directory replication process.
4. The tool requests replication of directory data, specifically targeting credential information. This involves using the DS-Replication-Get-Changes or similar replication-right GUIDs.
5. The Active Directory server responds by providing the requested data, which includes password hashes and other sensitive information.
6. The attacker extracts the credential information from the replicated data.
7. The attacker uses the extracted credentials to move laterally within the network and access other systems or data.
8. The attacker achieves their final objective, such as data exfiltration, ransomware deployment, or long-term persistence.

Impact

A successful DCSync attack can lead to the compromise of the entire Active Directory domain. This can result in widespread data breaches, loss of sensitive information, and significant disruption to business operations. Attackers can gain access to critical systems and data, potentially leading to financial losses, reputational damage, and legal liabilities. The number of potential victims is dependent on the size of the compromised Active Directory environment.

Recommendation

• Enable “Audit Directory Service Access” to generate the necessary Windows Security Event Logs (event code 4662) as described in the setup instructions.
• Deploy the Sigma rule “Detect First Time DCSync Activity” to your SIEM and tune for your environment to identify suspicious DCSync behavior.
• Investigate any alerts generated by the Sigma rule, focusing on the SubjectUserSid, SubjectUserName, Properties, AccessMask, and computer_name fields in the Windows Security Event Logs.
• Monitor for changes to Active Directory object permissions (5136 events) that could grant unauthorized users DCSync capabilities as outlined in the triage and analysis steps.