In recent years, the cybersecurity landscape has witnessed a surge in novel attack techniques that target authentication mechanisms in Windows environments. Kerberos Authentication Service Response (AS-REP) Roasting, a technique similar to Kerberoasting, has gained prominence as a method for attackers to compromise Active Directory (AD) authentication systems. This article provides an in-depth analysis of AS-REP Roasting, the tools attackers commonly employ, and effective mitigation strategies to defend against this threat.
AS-REP Roasting is an attack technique that targets the Kerberos authentication protocol, which is a fundamental component of Microsoft’s Active Directory. Kerberos is used to authenticate users and services within a Windows domain environment. AS-REP Roasting takes advantage of a vulnerability in how Kerberos processes certain types of authentication requests, enabling attackers to retrieve password hashes for user accounts with pre-authentication disabled.
Pre-authentication is a security feature in Kerberos that requires users to prove their identity before attempting to authenticate. However, certain accounts, such as service accounts, might have pre-authentication disabled for legitimate reasons. Attackers exploit this by sending a specific type of request to the domain controller, asking for a “ticket” for a specific user account. The domain controller responds with an encrypted ticket that contains the user’s password hash, which can then be decrypted offline by the attacker. A more technical breakdown in difference would be that a Kerberoasting attack has AS-REQ/AS-REP AND TGS-REQ/TGS-REP. AS-REP Roasting ONLY has AS-REQ/AS-REP. That is because Kerberoasting requests a Service Account Authorization Ticket, whereas AS-REP only requests a Kerberos Authentication Ticket.
Several tools are commonly used by attackers to perform AS-REP Roasting attacks:
There are two distinct methods by which the attack can be executed. In the scenario where the account’s username is known or guessed, the AS-REP Roasting technique can be leveraged by utilizing solely the account name. This approach empowers malicious entities to systematically probe widely-used names, employing brute-force strategies to potentially unveil usernames. A concrete representation of this concept can be observed in Figure 1, wherein the developers of CrackMapExec provide an example of an AS-REP Roasting attack.
Conversely, an alternative approach to executing the attack involves authentication. If active credentials are accessible within a specific domain, this avenue enables the acquisition of hash values for susceptible accounts, thereby laying bare their vulnerabilities. This process is demonstrated in Figure 2, depicting the outcome of an authentication-based attack.
To defend against AS-REP Roasting attacks and similar Kerberoasting techniques, organizations should implement a combination of proactive measures and monitoring practices:
AS-REP Roasting is a sophisticated attack technique that targets weaknesses in the Kerberos authentication protocol, allowing attackers to compromise user account password hashes. Understanding the mechanics of AS-REP Roasting and the tools attackers use is crucial for building effective defenses. By implementing a combination of technical measures, security best practices, and proactive monitoring, organizations can significantly reduce the risk of falling victim to AS-REP Roasting and similar authentication-based attacks. Regular security assessments and staying informed about emerging threats are also essential components of a robust cybersecurity strategy.
Kyle brings over seven years of experience in cybersecurity focusing on network penetration testing, social engineering, and physical security assessments. Kyle attended Ferris State University, graduating with a bachelor's degree in "Information Security and Intelligence" and actively holds Security+ and Network+ certifications. Kyle was the fastest in his previous company's history to work up to go from a junior-level penetration tester to a senior.
Kyle helps clients uncover hidden exposures and gain fresh insights that improve their security posture by keeping up to date with cutting edge attacks.
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