Daniel Petri

Active Directory (AD) is the cornerstone of most enterprise networks, providing centralized authentication, authorization, and access control to a myriad of resources. However, the complexity of AD configuration often makes the service a prime target for malicious actors looking to exploit weaknesses in an organization’s security posture. Several misconfigurations—for example, the misuse of a built-in functionality in AD that is responsible for some AD replication—can lead to such vulnerabilities. By manipulating this powerful feature, attackers can gain access to sensitive data, specifically to password hashes, that are stored in the AD database on domain controllers (DCs).

What is a DCSync attack?

A DCSync attack is a method that bad actors can use to impersonate a DC by leveraging the Directory Replication Services (DRS) Remote Protocol to request password data from a targeted DC. By design, DRS Remote Protocol enables efficient synchronization of directory services objects and their attributes across all DCs in an AD forest. However, attackers can weaponize this functionality to gain unauthorized access to user credentials and potentially escalate their privileges within the network.

Although this functionality is fundamental to the proper replictaion of an AD environment, only a limited number of security principals should have the necessary rights to perform these actions. Unfortunately, misconfigurations or lack of awareness can lead to the assignment of these rights to non-default security principals, creating a potential security risk.

How can incorrect AD replication rights impact security?

By default, specific rights are granted through the Replicating Directory Changes and Replicating Directory Changes All extended rights within AD. These rights permit a security principal to replicate directory objects and their attributes, including sensitive password data, from one DC to another. Although these rights are necessary for legitimate replication purposes, malicious actors can exploit the rights to perform DCSync attacks, exfiltrating password hashes and other sensitive information from the DC.

The impact of such an attack can be severe. DCSync attacks can enable attackers to impersonate legitimate users, escalate privileges, and move laterally within the network. In worst-case scenarios, the attacker can gain domain administrator privileges and take complete control of the AD infrastructure.

What tools can attackers use to mount a DCSync attack?

Several tools are currently available for mounting a DCSync attack:

  • Mimikatz is a powerful post-exploitation tool that can extract plaintext passwords, hashes, and Kerberos tickets from memory. This tool includes a DCSync module that threat actors can use to perform DCSync attacks and extract password hashes from DCs.
  • Impacket is a collection of Python classes for working with network protocols. This tool includes a script called secretsdump.py that enables DCSync attacks.
  • PowerShell Empire is a post-exploitation framework that provides a variety of modules for offensive security operations. One of the modules, Invoke-DCSync, enables DCSync attacks.

Identifying default security principals with incorrect replication rights

By default, these rights are assigned to a limited number of security principals, typically including:

  • Domain Admins
  • Enterprise Admins
  • Administrators
  • Domain Controllers
  • Read-only Domain Controllers

These security principals are usually trusted and have the necessary privileges to perform directory replication tasks within the domain. The risk arises when non-default security principals are inadvertently granted replication rights, providing an opportunity for attackers to exploit the feature.

Look for accounts that are delegated the following rights:

  • Replicating Directory Changes (DS-Replication-Get-Changes)
  • Replicating Directory Changes All (DS-Replication-Get-Changes-All)
  • Replicating Directory Changes in Filtered Set (DS-Replication-Get-Changes)

Determine whether DCSync is being used to host other DCs and determine whether any accounts that aren’t members of Domains Admins or Domain Controllers have these rights.

Techniques for discovering non-default security principals with replication rights

To proactively identify and manage the risk associated with a DCSync attack, it’s essential to monitor and audit your AD environment for non-default security principals that possess these rights. You can employ several methods:

  • Use built-in AD tools like ACL Diagnostics or Ldp to query the access control lists (ACLs) on the domain object.
  • Leverage PowerShell scripts to enumerate security principals with DCSync rights.
  • Implement auditing solutions that specialize in detecting AD misconfigurations and security risks, such as Purple Knight.

Best practices for mitigating risks associated with DCSync attack

To minimize the risks associated with DCSync attack, consider implementing these best practices:

  • Limit the number of security principals with replication rights to only those that absolutely require those rights.
  • Regularly review and audit your AD environment to identify non-default security principals with these rights and remove any unnecessary permissions.
  • Implement the principle of least privilege, ensuring that users and groups have only the minimum level of access required to perform their tasks.
  • Use strong and unique passwords for all privileged accounts to reduce the risk of credential compromise.
  • Continuously monitor and log security events within your AD environment to detect and respond to potential threats in a timely manner.

Training and awareness for IT staff and security teams

It is essential to educate IT staff and security teams about the potential risks associated with these rights. By raising awareness to this potential attack, you increase your AD environment security posture. Conduct regular training sessions and workshops to ensure that your teams are up to date with the latest security best practices, threat intelligence, and effective defense strategies.

Keeping up with the latest threat intelligence

The threat landscape is constantly evolving. Staying informed about the latest threats and attack techniques is crucial for maintaining a secure AD environment. Subscribe to industry news, security blogs, and threat intelligence feeds to keep abreast of emerging threats, vulnerabilities, and best practices. Share this information with your IT staff and security teams to ensure that they remain vigilant and prepared to counter potential DCSync attacks.

In summary, defending your AD environment against DCSync attacks (as well as the other threats) necessitates a comprehensive strategy. This involves conducting regular audits, adhering to best practices, investing in education and awareness initiatives, and keeping up to date with the most recent threat intelligence. By proactively addressing security concerns, you can effectively mitigate the risks associated with DCSync rights, ensuring the protection of your organization’s invaluable resources.

Learn more about AD security