Kerberoasting

Kerberoasting is a sophisticated attack method that exploits the Kerberos authentication protocol integral to Active Directory (AD). Kerberos is designed to facilitate secure authentication over potentially insecure networks, and becomes an unwitting accomplice in these attacks, providing a backdoor through which attackers can gain unauthorized access to sensitive systems and data.

Kerberoasting specifically targets service accounts within an AD environment, exploiting the fact that any authenticated user can request Ticket Granting Service (TGS) tickets for any service.

Attackers leverage this functionality to request TGS tickets associated with Service Principal Names (SPNs), then work offline to crack the encrypted tickets and extract service account passwords. This technique allows attackers to bypass network defenses and gain access to restricted areas undetected.

The threat posed by Kerberoasting is significant due to its stealthy nature and the potential for high-impact breaches. Organizations leveraging AD for network authentication and authorization must be aware of this threat vector to implement effective defenses.

Understanding Kerberoasting — its mechanisms, implications, and prevention strategies — is crucial for cybersecurity and IT professionals tasked with defending their organizations’ digital assets.

How Kerberoasting Works

Kerberoasting exploits the Kerberos authentication protocol, which is a core aspect of Active Directory (AD) used for authenticating users and services in a network. Understanding this attack requires a foundational grasp of Kerberos itself, which operates on a ticket-based mechanism to ensure secure communications across a network.

The Kerberos Authentication Protocol

At the heart of Kerberos is the Ticket Granting Ticket (TGT), obtained upon a user’s successful login. The TGT is then used to request Ticket Granting Service (TGS) tickets for accessing various network services. These services are identified by their Service Principal Names (SPNs). It’s a system designed for security, but its architecture inadvertently opens a door for exploitation.

The Attack Vector

Kerberoasting takes advantage of the fact that any authenticated user within a domain can request TGS tickets for any service defined under an SPN. By posing as a legitimate user, an attacker requests TGS tickets for services, which are encrypted using the password of the service account. This attack relies on the attacker’s ability to take these encrypted tickets offline and attempt to crack them in order to reveal the password of the service account.

This process involves the following steps:

1. Scanning for Service Accounts: Attackers scan the AD for user accounts with associated SPNs, which indicate service accounts.
2. Requesting TGS Tickets: Using a legitimate user’s credentials, attackers request TGS tickets from the AD domain controller for those identified service accounts.
3. Extracting and Cracking the Tickets: The attacker then extracts the encrypted part of the TGS tickets and uses offline brute force or password cracking tools to discover the service account’s password.

Why It’s Effective

Kerberoasting is particularly effective because it can be conducted with standard user privileges and without triggering alerts that might be associated with other forms of attack, such as direct password brute force attempts against the network. Moreover, the offline nature of the password cracking effort evades the detection mechanisms that networks typically employ to identify suspicious activities, such as multiple failed login attempts.

This attack underscores a critical vulnerability in the Kerberos protocol’s implementation within Windows AD environments — the reliance on the secrecy and strength of service account passwords. Given the silent and stealthy nature of Kerberoasting, it poses a significant threat to organizations, enabling attackers to gain access to sensitive services and data.

The Threat Landscape

In organizational networks, Kerberoasting attacks are common and successful, illustrating a critical vulnerability in cybersecurity. As attackers refine their methodologies, Kerberoasting remains an attractive exploit due to its combination of stealth and effectiveness. It is vital to understand how this threat operates in order to devise defenses that will be able to withstand its complexity.

Prevalence of Kerberoasting Attacks

Kerberoasting has become a common attack method, partly due to the ubiquity of Windows Active Directory (AD) in corporate environments and the relative simplicity of executing the attack. Tools like PowerSploit’s Invoke-Kerberoast module or Rubeus make these attacks accessible even to less technically sophisticated attackers. Real-world incidents, including notable breaches attributed to state-sponsored actors and criminal groups, highlight the ongoing threat posed by Kerberoasting.

Factors Contributing to Kerberoasting’s Success

• Weak Password Policies: Service accounts often have weak or default passwords that are rarely changed, making them prime targets for Kerberoasting.
• Lack of Visibility and Monitoring: Many organizations lack the necessary visibility into their AD environment to detect the early signs of a Kerberoasting attack.
• Misconfiguration and Overprivileged Accounts: Improperly configured service accounts and those with unnecessary privileges expand the attack surface for Kerberoasting.
• Stealthiness: Kerberoasting attacks are difficult to detect because they don’t require elevated privileges and can be performed without triggering multiple failed authentication attempts, which are commonly monitored for.

Examples of Kerberoasting Attacks

Kerberoasting attacks have been a part of some of the most sophisticated cyber attacks observed in recent years, demonstrating the high stakes involved when organizations fail to secure their Active Directory (AD) environments adequately.

Operation Wocao

In one notable example, the threat actors behind Operation Wocao utilized the PowerSploit framework’s Invoke-Kerberoast module to perform Kerberoasting attacks. This operation showcased the attackers’ ability to request encrypted service tickets and subsequently crack the passwords of Windows service accounts offline.

The breached accounts were then used for lateral movement within networks, enabling further exploitation and access to sensitive information. This incident underlines the effectiveness of Kerberoasting in advanced persistent threat (APT) campaigns, highlighting the importance of securing service accounts against such attacks​ (MITRE ATT&CK)​.

SolarWinds Compromise

Another significant case involved the SolarWinds breach, where attackers leveraged Kerberoasting among other techniques to gain access to networks. In this instance, attackers obtained Ticket Granting Service (TGS) tickets for Active Directory Service Principal Names (SPNs) and cracked them offline to escalate their access privileges.

This compromise not only highlighted the vulnerability of service accounts to Kerberoasting but also the potential for wide-reaching implications, as the breach impacted numerous high-profile organizations and government agencies​ (MITRE ATT&CK)​.

Wizard Spider’s Use of Kerberoasting

The criminal group known as Wizard Spider has been reported to use Kerberoasting as part of their arsenal. They employed tools like Rubeus and Mimikatz to steal AES hashes and service account credentials through Kerberoasting. This technique allowed them to maintain access and control over compromised networks, facilitating the deployment of ransomware and other malicious payloads. The activities of Wizard Spider exemplify the criminal exploitation of Kerberoasting, underscoring the risk to organizations across sectors​ (MITRE ATT&CK)​.

These examples of Kerberoasting attacks illustrate the critical need for organizations to monitor and secure their AD environments actively. The sophistication and diversity of attackers leveraging this technique—from state-sponsored APT groups to criminal collectives—underscore the importance of robust security measures, including strong password policies, regular auditing of service accounts, and the implementation of detection mechanisms to identify suspicious activities indicative of Kerberoasting attempts.

Detecting and Preventing Kerberoasting

In order to detect and prevent Kerberoasting, which exploits legitimate features of the Kerberos authentication protocol for malicious purposes, a multifaceted approach is required.

Organizations can significantly reduce their vulnerability to Kerberoasting through strategic planning, robust security protocols, and continuous monitoring.

Best Practices for Prevention

• Leverage Identity-Based Zero Trust Security policies: By implementing a Zero Trust security model, you can ensure that no entity within the network is trusted by default, regardless of its location within the perimeter. This principle applies to both human users and service accounts, and by requiring verification at every access attempt, you can reduce the attack surface available to adversaries, including those attempting Kerberoasting.
• Implement Strong Password Policies: Enforce complex, lengthy (ideally 25+ characters), and regularly changed passwords for all accounts, especially service accounts with Service Principal Names (SPNs). Utilizing tools like password managers and Group Managed Service Accounts (gMSAs) can help maintain strong password hygiene without sacrificing operational efficiency​.
• Enable Multi-Factor Authentication (MFA): Adding an extra layer of security through MFA can significantly reduce the risk of unauthorized access, even if service account credentials are compromised. MFA should be standard for all user accounts, not just those with elevated privileges​.
• Adhere to the Principle of Least Privilege (PoLP): Ensure that accounts, especially service accounts, have only the permissions necessary for their functions. Limiting access rights minimizes the potential damage an attacker can do if they compromise an account​.
• Develop a Comprehensive Identity Security Strategy: A robust identity and access management framework can safeguard against various threats, including Kerberoasting. This strategy should include regular audits of service accounts, privileged access management (PAM), and the adoption of security solutions that provide visibility into and control over account use​.

Techniques for Detecting Kerberoasting

• Monitor for Anomalous Kerberos Activity: Implement logging and monitoring to detect unusual patterns of Kerberos authentication requests, such as a high volume of TGS requests for SPNs within a short time frame.
• Audit Service Account Usage: Regularly review service account activity for signs of unauthorized use, such as accessing services or data outside of normal patterns. This review can help identify compromised accounts before they are used for lateral movement or data exfiltration.
• Leverage Advanced Security Analytics: Utilizing machine learning and behavior analysis can help identify subtle signs of Kerberoasting, distinguishing between legitimate service account use and potentially malicious activity.