What is Unconstrained Delegation ?

Unconstrained Delegation is a feature within Active Directory environments that allows designated services to act on behalf of users, requesting access to other network resources without requiring additional authentication. This delegation model grants specified services a broad authority, making them trusted to impersonate any user to any service.

Unconstrained delegation is the insecure legacy version of Kerberos Delegation which was later followed by constrained delegation and eventually resource-constrained delegation. This capability is intended to streamline service interactions, particularly in complex, multi-tiered network architectures where services must communicate across boundaries securely and efficiently.

How Unconstrained Delegation Works

At its core, Unconstrained Delegation operates by leveraging Kerberos tickets. When a user authenticates to a service enabled for Unconstrained Delegation, the Key Distribution Center (KDC) issues a Ticket-Granting Ticket (TGT) along with the usual service ticket. This TGT, which effectively proves the user’s identity, can then be presented by the service to the KDC to request tickets to other services on behalf of the user. This process allows for seamless access across services without repeated user authentication prompts.

However, Unconstrained Delegation contrasts sharply with its more restrictive counterpart, Constrained Delegation. While Unconstrained Delegation places no limitations on the services to which the delegated service can request access on behalf of the user, Constrained Delegation tightly controls this by specifying exactly which services are accessible.

This distinction is crucial for security planning, as the broader permissions associated with Unconstrained Delegation pose a greater risk if misconfigured or exploited by malicious actors.

The use of Unconstrained Delegation is typically reserved for scenarios where services require extensive cross-domain interactions that cannot be efficiently managed through Constrained Delegation. Examples include highly integrated application environments and situations where services need to perform wide-ranging actions across various network segments on behalf of users.

Despite its utility, the security implications of granting such wide-reaching delegation rights necessitate careful consideration and management to prevent abuse.

The Risks Associated with Unconstrained Delegation

The utility of Unconstrained Delegation, particularly in complex IT environments, is undeniable. However, its broad permissions model introduces substantial security risks, making it a target for exploitation in cyber attacks. The primary concern with Unconstrained Delegation revolves around its potential misuse for lateral movement and privilege escalation within a network.

One of the most significant risks is that if an attacker compromises a service account enabled for Unconstrained Delegation, they gain the ability to request access tokens for any other service on behalf of any user.

This capability can be abused to access sensitive information or perform unauthorized actions across the network, effectively turning a single compromised account into a gateway for widespread network penetration. This scenario is especially concerning in environments where service accounts with Unconstrained Delegation privileges have not been properly secured or monitored.

The exploitation of Unconstrained Delegation can also facilitate the execution of sophisticated cyber attacks, including Kerberoasting. Kerberoasting takes advantage of the Kerberos protocol’s use of weak encryption for certain aspects of ticket exchange.

Attackers can request service tickets on behalf of any user for services enabled for Unconstrained Delegation, then attempt to crack the tickets offline to discover service account passwords. This attack vector underscores the importance of strong, complex passwords for service accounts and highlights the risks associated with Unconstrained Delegation.

Another layer of risk is introduced by the inherent complexity and administrative overhead required to securely manage Unconstrained Delegation settings. Misconfigurations can inadvertently expose services to unauthorized access, and the dynamic nature of IT environments means that what is secure today may not be tomorrow. Continuous vigilance, regular audits, and a deep understanding of the delegation settings and their implications are necessary to mitigate these risks.

Real-world incidents have illustrated the dangers of improperly managed Unconstrained Delegation. Attackers have exploited it to move laterally within networks, escalate their privileges, and inflict significant damage to organizational IT infrastructures. These incidents serve as stark reminders of the potential consequences of overlooking the security implications of Unconstrained Delegation.

Best Practices for Secure Delegation

Securing Unconstrained Delegation necessitates a multifaceted approach, focused on minimizing its inherent risks while leveraging its functionality. Adopting best practices is essential for organizations aiming to balance operational requirements with robust security measures.

Here are strategic practices to enhance the security of Unconstrained Delegation:

1. Employ Constrained Delegation Wherever Possible

Transitioning to Constrained Delegation provides a tighter security model by explicitly limiting the services to which a delegated account can present delegated credentials. This limitation significantly reduces the risk of unauthorized access through delegation, making it a preferred alternative to Unconstrained Delegation whenever feasible.

2. Regular Audits and Monitoring

Continuous monitoring and periodic audits of delegation settings are crucial. Organizations should implement solutions that provide visibility into how delegated permissions are being used and by whom. Regular reviews help identify misconfigurations or unnecessary delegation permissions that could expose the network to risks.

3. Apply the Principle of Least Privilege

Minimize the number of accounts with Unconstrained Delegation permissions and ensure that these accounts possess only the necessary privileges for their intended functions. This practice limits the potential damage an attacker can inflict if they compromise a delegated account.

4. Use Strong Authentication Mechanisms

Enhancing the authentication requirements for accounts with delegation permissions adds an additional layer of security. Implementing Multi-Factor Authentication (MFA) and strong password policies for these accounts can help protect against credential theft and misuse.

5. Segmentation of Network Resources

Network segmentation can limit the scope of lateral movement in case of an account compromise. By dividing the network into segments with controlled access, organizations can reduce the reach of accounts with Unconstrained Delegation and contain potential breaches more effectively.

6. Implementing Advanced Security Solutions

Utilizing advanced security solutions that can detect and respond to anomalous activities associated with Unconstrained Delegation can significantly enhance protection. Solutions that offer Identity Threat Detection and Response (ITDR) capabilities can identify suspicious patterns of behavior related to delegation, such as abnormal access requests, and provide real-time mitigation.

7. Education and Awareness

Ensuring that IT and security teams are aware of the risks associated with Unconstrained Delegation and understand the best practices for its secure use is fundamental. Regular training sessions can help maintain a high level of vigilance and ensure that security considerations are integrated into the management of delegation settings.

By integrating these best practices into their security strategies, organizations can mitigate the risks associated with Unconstrained Delegation, ensuring that the convenience and functionality it offers do not come at the expense of network security.

Finding Where Unconstrained Delegation Has Been Enabled

Finding where Unconstrained Delegation has been enabled in your Active Directory (AD) environment is crucial for understanding potential security risks and ensuring your network’s integrity. Here’s a systematic approach to identify these configurations:

Using PowerShell

PowerShell is a powerful tool for managing and querying Active Directory environments. You can use it to find accounts with Unconstrained Delegation enabled by executing a simple script.

  1. Open PowerShell with Administrative Privileges: Launch PowerShell as an administrator to ensure you have the necessary permissions to query AD.
  2. Import the Active Directory Module: If not already available by default, you might need to import the Active Directory module with the command: Import-Module ActiveDirectory
  3. Execute a Query to Find Unconstrained Delegation: Use the Get-ADUser and Get-ADComputer cmdlets to search for user and computer accounts where the TrustedForDelegation property is True. This property being True indicates that Unconstrained Delegation is enabled. Here’s how you can structure the command: Get-ADUser -Filter ‘TrustedForDelegation -eq $true’ -Properties TrustedForDelegation | Select-Object Name, DistinguishedName, TrustedForDelegation
    And for computer accounts: Get-ADComputer -Filter ‘TrustedForDelegation -eq $true’ -Properties TrustedForDelegation | Select-Object Name, DistinguishedName, TrustedForDelegation
  4. Review the Output: The commands will list the AD users and computers that have Unconstrained Delegation enabled. Pay close attention to these accounts, as they possess significant permissions that could be exploited if compromised.

Using Active Directory Users and Computers (ADUC)

For those who prefer a graphical user interface (GUI), the Active Directory Users and Computers (ADUC) tool can be used:

  1. Open ADUC: Ensure you have the necessary administrative privileges to access and modify AD objects.
  2. Enable Advanced Features: Go to the “View” menu and ensure that “Advanced Features” is checked. This option reveals additional properties for AD objects.
  3. Search for Accounts with Unconstrained Delegation: Navigate through your AD structure and inspect the properties of user and computer accounts. Under the “Delegation” tab, accounts with Unconstrained Delegation will have “Trust this user for delegation to any service (Kerberos only)” selected.
  4. Document and Review: Keep a record of all accounts with Unconstrained Delegation enabled for further review and possible action.