Kerberoasting: A Gateway to Privilege Escalation in Enterprise Networks

Hackers in today's digital world are constantly creating innovative ways to access systems and steal data, especially in more interconnected business networks. A particularly effective method they use is referred to as "Kerberoasting." The success of this attack path in using flaws in the Kerberos authentication system directly leads to the serious privilege escalation assaults it may cause in corporate settings. Companies, security practitioners, and IT experts who want to guard their systems from this increasing threat must be informed about Kerberoasting.

The Basics of Kerberos Authentication

Kerberos is a widely used network authentication protocol that relies on secret-key cryptography to verify the identity of users and systems within a network. It was developed in the 1980s by MIT to authenticate users securely across unprotected networks, including the Internet. Windows Active Directory (AD), which Microsoft ultimately made Kerberos the default for, is the popular authentication technique used in business networks nowadays. Kerberos generates a Ticket Granting Ticket (TGT) once a user has successfully authenticated. Service requests using this TGT provide access to email systems, file servers, and databases, among other network resources. Only authorized users may access the resources these service tickets contain, including the Service Principal Name (SPN), by encrypting them with the password hash of the service account.

The Rise of Kerberoasting

One kind of attack using Kerberos's service ticket issuance system is kerberoasting. Accounts with SPNs are the ones it targets since they are linked to highly privileged service accounts, including those handling email servers, database services, or enterprise-level apps. Weak or poorly kept passwords make these service accounts easy targets for hackers. Starting from the domain controller, an attacker asks for a service ticket for a target account using a quite low-privileged user. Since the password is encrypted with the hash of the target account, the assailant can try brute force or crack the password offline using multiple techniques once he gets the service ticket. Once the security of the target service account is compromised, the assailant could access other significant systems on the network and maybe unlock more permissions.

How Kerberoasting Works

• Step 1 - User Enumeration: The attacker first identifies service accounts that have SPNs registered in Active Directory. These accounts typically run critical services and may have elevated privileges. Tools like PowerView are used to query the domain and retrieve associated SPNs for service accounts.

• Step 2 - Ticket Request: The attacker, using low-privileged credentials, requests a Kerberos service ticket for the targeted service account. The domain controller generates the ticket, encrypts it with the service account's password hash, and sends it to the attacker. At this stage, the attacker has an encrypted ticket but not direct access to the service.

• Step 3 - Cracking the Ticket: The attacker attempts to crack the service ticket offline. Since it is encrypted with the service account's password hash, brute-force tools like HashCat or John the Ripper are used to crack the password. If the password is weak, the attacker can eventually recover it and gain access to the service account.

• Step 4 - Privilege Escalation: With the recovered password, the attacker can escalate their privileges within the network. Since service accounts often have higher permissions, the attacker may gain access to critical systems, enabling lateral movement across the network and potentially obtaining domain admin privileges or access to sensitive data.

  Impacts of Kerberoasting Attacks

Kerberos causes major concern for businesses as it makes it easy for attackers to expand rights. Regular usage of it is part of larger all-encompassing attack campaigns like Advanced Persistent Threat (APT) operations. Once an adversary has increased their access, they can install malware, steal sensitive data, or even control the full network of a company. The 2017 NotPetya assault, costing billions of dollars and aiming businesses all across the world, is one well-known instance of Kerberoasting in action. The attackers spread malware over corporate networks via Kerberoasting and other methods, therefore compromising significant infrastructure and interfering with business processes.

During a penetration test for a major financial institution, Kerberoasting enabled a security company to access critical banking apps operating on service accounts in another context. The effective results of this assault are shown by the testers' successful entry of significant financial systems via weak passwords.

Why Kerberoasting Is Effective

In particular, kerberoasting is effective because a direct connection with the target system is not required once the service ticket is obtained. As the assault depends on internet connectivity, the assailant might operate at their own speed to breach passwords without attracting notice from intrusion detection systems. Moreover, the attack uses architectural flaws in the Kerberos system, making discovery or counteraction challenging in the absence of comprehensive security monitoring and management. Furthermore, poor password management for service accounts contributes to Kerberoasting's success. When it comes to updating passwords, service accounts are usually neglected, and they usually have weak and readily cracked passwords. Companies with several service accounts, each accessing various systems, may find it difficult to enforce consistently strong password restrictions, therefore increasing the likelihood of security breakdowns.

Defending Against Kerberoasting

Given the severity of Kerberoasting attacks, organizations must implement effective countermeasures to protect their networks. Here are some best practices that can help mitigate the risk.

• Strong Password Policies: Ensuring that service accounts use strong, complex passwords is the first line of defense against Kerberoasting. Organizations should enforce password policies requiring long, unique passwords that are rotated regularly. Tools like Microsoft’s Local Administrator Password Solution (LAPS) can automate password management.

• Monitoring and Detection: Detecting Kerberoasting requires constant monitoring of network traffic and log files for suspicious activity. Security Information and Event Management (SIEM) systems can identify unusual patterns, such as an increase in Kerberos ticket requests or abnormal login attempts. Real-time monitoring solutions are crucial for early threat detection.

• Account Privilege Segmentation: Organizations should minimize the number of highly privileged service accounts and limit their use to essential tasks. Service accounts should have the minimum necessary access and privileged accounts should be segmented from ordinary users to prevent lateral movement during an attack.

• Use of Managed Service Accounts (MSAs): Managed Service Accounts (MSAs) are a Windows Server security feature that provides automatic password management and reduces the risk of Kerberoasting. MSAs automatically generate and update passwords, keeping them strong and secure without manual intervention.

• Implementing Multi-Factor Authentication (MFA): Although MFA does not directly mitigate Kerberoasting, it adds an additional layer of security, making it harder for attackers to move laterally across a network after compromising a service account. Enforcing MFA for critical systems and services reduces the overall impact of a successful attack.

  Conclusion

  Kerberoasting represents a significant risk to modern enterprise networks, particularly in environments where Kerberos is the primary authentication protocol. By exploiting inherent vulnerabilities in the way Kerberos handles service tickets, attackers can escalate privileges and potentially compromise entire networks. To defend against this threat, organizations must adopt strong password policies, monitor for suspicious activity, limit the use of privileged service accounts, and implement advanced security measures like MSAs and MFA. In an era where cyber threats continue to evolve, staying informed and proactive is key to securing enterprise systems from privilege escalation attacks like Kerberoasting.