Cybersecurity professionals often face intricate challenges when evaluating Active Directory environments, especially when dealing with cross-forest trust relationships. These trusts, while crucial for enabling collaboration between different domains, can also become a significant attack vector for malicious actors. This detailed write-up delves into the exploitation of domain trusts, focusing particularly on cross-forest Kerberoasting and foreign group membership enumeration, utilising tools such as Impacket and BloodHound-python.

A Practical Approach to Cross-Forest Kerberoasting

Kerberoasting is a well-established attack technique that targets Service Principal Names (SPNs) within an Active Directory to extract Ticket Granting Service (TGS) tickets for offline cracking. When this method is applied across a forest trust, it can yield substantial results. By using GetUserSPNs.py from Impacket on a Linux host, attackers can list SPNs in a trusted domain by exploiting credentials from an account with authentication privileges in the target domain.

Steps to Execute Cross-Forest Kerberoasting

1. Enumerate SPNs:
   • Run the GetUserSPNs.py script with the -targetdomain flag to identify SPNs in the trusted domain. For example:

GetUserSPNs.py -target-domain FREIGHTLOGISTICS.LOCAL

1. This command might reveal accounts.
2. Request TGS Tickets:
   • Add the -request flag to obtain TGS tickets for offline cracking. Optionally, use the -outputfile flag to save the ticket for further processing:

GetUserSPNs.py -request -target-domain FREIGHTLOGISTICS.LOCAL

3. Crack Tickets Offline:
   • Use tools like Hashcat with mode 13100 to crack the extracted TGS tickets. If successful, attackers gain access to privileged accounts in the target domain.

Potential Impact

A cracked password can allow attackers to authenticate as a Domain Admin in the target domain. Additionally, if passwords are reused across domains, it may enable lateral movement or privilege escalation within the current domain, underscoring the importance of iterative testing and thorough enumeration.

Foreign Group Membership Enumeration with BloodHound-python

Another critical aspect of exploiting trust relationships involves identifying users or administrators from one domain who hold privileged memberships in another domain. BloodHound-python simplifies this process by collecting and analysing data from multiple domains.

Setup and Execution

1. Configure DNS:
   • Ensure proper DNS resolution by editing /etc/resolv.conf on the Linux attack host:
2. Run BloodHound-python:
   • Execute the tool against the target domain:
   • This gathers data on domains, users, groups, computers, and trusts.
3. Analyse Results:
   • Compress JSON files into a ZIP archive and upload them to the BloodHound GUI for analysis:

Key Insights

BloodHound’s analysis can uncover dangerous rights, such as foreign group memberships that grant administrative privileges across domains. For instance, a built-in Administrator account in one domain might be part of the Administrators group in another domain because of bidirectional forest trusts.

Closing Thoughts on Trust Exploitation

Domain trusts are essential for the functionality of Active Directory but can introduce significant security risks if not managed properly. Adversaries can exploit these relationships to escalate privileges or compromise additional domains through techniques like Kerberoasting and foreign group membership enumeration.

Mitigation Strategies:

• Regularly audit trust relationships.
• Enforce strong password policies and avoid reuse across domains.
• Monitor privileged account activity across forests.

Understanding and addressing these vulnerabilities is vital for maintaining secure Active Directory environments amidst changing threats.

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