Kerberoasting: Uncovering Hidden Risks in Active Directory

Introduction

Kerberoasting is a sophisticated attack technique that takes advantage of vulnerabilities in the Kerberos authentication protocol within Microsoft Active Directory environments. By targeting service accounts associated with Service Principal Names (Service Principal Names (SPNs)), attackers can extract encrypted credentials and attempt to crack them offline. A successful attack can lead to unauthorized access to high-privilege accounts, enabling lateral movement and escalating the impact of a breach.

This guide offers a detailed exploration of Kerberoasting, including the mechanics of the attack, the tools used—particularly the open-source tool Rubeus—and practical mitigation strategies. Whether you’re a risk manager seeking to evaluate organizational vulnerabilities or a security professional aiming to strengthen defenses, this article provides actionable insights to address this pervasive threat.

Understanding Kerberoasting

Kerberoasting targets the authentication process of service accounts in Active Directory. These accounts are often tied to SPNs, which identify network services within the Kerberos protocol. When a client requests access to a service, the Key Distribution Center (KDC), a critical component of Kerberos responsible for managing tickets and authenticating users, issues a ticket-granting service (TGS) ticket encrypted with the service account's NTLM (NT LAN Manager) hash, which is part of Microsoft's suite of security protocols for authentication. Attackers exploit this mechanism by requesting these tickets, extracting them, and cracking their encryption offline.

A 2018 campaign highlighted the risks of Kerberoasting, where attackers used weak encryption and poor password practices to compromise organizations. These incidents underline the importance of securing service accounts and regularly auditing SPNs.

For more details, see this comprehensive guide on Service Principal Names (SPNs) and another on the Key Distribution Center (KDC).

Rubeus: A Tool for Kerberos Exploitation

Rubeus is an open-source, C#-based tool designed to interact with and abuse the Kerberos protocol. Created by renowned security researcher Will S. as part of the GhostPack suite, Rubeus has become an indispensable tool for penetration testers and red teams. Its ease of use and powerful capabilities have also drawn the attention of malicious actors, making it a double-edged sword in the cybersecurity landscape.

Key Features of Rubeus:

• Automated Kerberos Attacks: Rubeus simplifies attacks like Kerberoasting, pass-the-ticket, and ticket renewal.
• Seamless Integration: Designed for Windows environments, it leverages .NET frameworks for compatibility.
• Customizable Commands: Users can tailor attacks to specific scenarios, making Rubeus highly versatile.

How to Obtain Rubeus:

Rubeus is freely available on GitHub: GitHub - Rubeus. To use it, download the source code and compile it or obtain precompiled binaries from trusted sources. Always verify the integrity of binaries and ensure compliance with ethical guidelines and legal permissions before deploying Rubeus.

Demonstrating Kerberoasting with Rubeus

A step-by-step demonstration of Kerberoasting using Rubeus can provide valuable insights into how attackers exploit these vulnerabilities.

Step 1: Enumerate SPNs

Run the following PowerShell command to retrieve accounts tied to SPNs:

Get-ADUser -Filter {ServicePrincipalName -ne "$null"} -Properties ServicePrincipalName        

Step 2: Request Service Tickets

Use Rubeus to request Kerberos TGS tickets for the identified SPNs:

Rubeus.exe kerberoast /outfile:hashes.txt        

Step 3: Crack Hashes

Analyze the extracted ticket hashes using a password-cracking tool like Hashcat, a powerful open-source password recovery tool, designed to efficiently crack password hashes using multiple algorithms. Learn more about Hashcat here.:

hashcat -m 13100 hashes.txt wordlist.txt        

What Is a Wordlist?

A wordlist, such as "wordlist.txt," is a dictionary of potential passwords used during cracking attempts. Popular wordlists include RockYou, which contains leaked passwords from real-world breaches, and custom lists tailored to specific environments. Wordlists can be downloaded from repositories like SecLists. SecLists is a comprehensive collection of security-related wordlists, including those for password cracking, fuzzing, and reconnaissance. To choose the most appropriate wordlist for your needs, consider the context of your environment—whether targeting commonly used passwords, organization-specific patterns, or leaked credential datasets. Experiment with different wordlists to ensure coverage of potential vulnerabilities.. Select a wordlist aligned with the types of passwords you aim to test.

Enhancing the Demonstration

To deepen insights from your demonstration:

• Experiment with a variety of wordlists, including industry-specific lists and leaked datasets, to simulate diverse cracking scenarios.
• Record the time taken to crack weak versus strong passwords and compare the computational effort.
• Test alternate techniques like hybrid attacks to measure their effectiveness.
• Review results for patterns, highlighting systemic issues like recurring weak passwords.

Interpreting the Results

Analyzing the output of the demonstration is crucial for understanding potential risks:

• Cracked Hashes: These indicate weak service account passwords. Each cracked password represents a vulnerability that could allow attackers to impersonate services or escalate privileges.
• Uncracked Hashes: While uncracked, these hashes may still represent risks if the passwords are only temporarily resistant due to computational limits.

Interpret the results to prioritize remediation efforts. Accounts with cracked passwords should be addressed immediately, and password policies should be reviewed and strengthened.

Mitigation Strategies

Combatting Kerberoasting effectively requires a combination of preventative measures and proactive monitoring. Consider implementing the following:

• Enforce Strong Password Policies: Require complex and lengthy passwords for all service accounts. Use automated password management tools to eliminate weak credentials.
• Implement Password Rotation: Rotate service account credentials regularly. Tools like Group Managed Service Accounts (gMSAs) can automate this process.
• Audit SPNs: Periodically review SPNs to ensure they are necessary and correctly configured. Remove or disable any unused accounts to reduce attack surfaces.
• Enhance Monitoring: Deploy Sysmon to log Kerberos-related activity and integrate with Security Information and Event Management (SIEM) systems to detect anomalies.
• Educate Staff: Train IT and security teams to recognize Kerberos-related threats and respond effectively. Awareness is a critical component of defense.

Conclusion

Kerberoasting exemplifies how attackers exploit authentication system weaknesses and poor password hygiene. By understanding its mechanisms and implementing robust defenses, organizations can mitigate this threat and strengthen their security posture.

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