What Is Kerberoasting? Attack Explained and How It Works

What is Kerberoasting?

Kerberoasting is a post-compromise attack technique for cracking passwords associated with service accounts in Microsoft Active Directory. The attacker impersonates an account user with a service principal name (SPN) and requests a service-related ticket. They then crack the password hash linked to that service account, log in with the plaintext credentials, and advance the attack.

Kerberoasting Key Takeaways:

• Kerberoasting is an attack method for cracking password hashes for service accounts in Active Directory.
• Password cracking takes place offline, helping attackers avoid detection, alerts, logging, or account lockouts.
• Once they log in, attackers appear as approved users and advance their attacks.
• It is difficult to preempt kerberoasting attacks since ticket requests are frequent, with anomalous ones hard to spot.
• MFA and centralized password management can help mitigate the kerberoasting threat.

Kerberoasting attackers crack password hashes offline using brute force methods. Working offline allows attackers to evade detection since no unusual activity or data transmission will trigger alerts or show up in logs. Also, since there is no use of malware, typical antivirus software cannot catch kerberoasting attacks.

With the plaintext credentials in hand, attackers appear to be legitimate account owners. This gives them access to the networks, systems, and assets to which the account owner typically has access. Since traditional cybersecurity solutions often don’t monitor the behavior of approved users, attackers have ample time and freedom to obtain other credentials, steal data, or set up routes to future access.

It is difficult to preempt kerberoasting attacks. Legitimate ticket requests are frequent, making it tough to spot suspicious ones. Also, there is no way to track whether login immediately follows the ticket request or not. This allows the attacker to work offline, cracking the password for as long as it takes without being locked out.

Some steps that can help limit the threat of kerberoasting:

• Use multifactor authentication (MFA).
• Use complex passwords for service accounts that use Kerberos with SPN values.
• Centrally manage passwords in Active Directory. Ensure that passwords are random, complex, changed often, and automatically rotated.
• Be on the lookout for unusually high levels of service ticket requests.
• Use tools to monitor abnormal account usage beyond login.

The Purpose of Kerberoasting

The objective of a Kerberoasting attack is to extract password hashes of user accounts stored in the AD domain. These password hashes can then be cracked to obtain the actual plaintext passwords of the user accounts, which can be used to gain access to sensitive information.

The attack is particularly effective against service accounts, which are user accounts that are used by services and applications to run with specific privileges. Service accounts are often highly privileged and have access to sensitive data, making them a valuable target for attackers.

How Kerberoasting Exploits Kerberos

In a Kerberoasting attack, the attacker identifies user accounts in the AD domain that have service principal names (SPNs) associated with them, indicating that the user has access to specific network services. The attacker then requests a service ticket for the user account, which contains the user's hashed password.

The Kerberos protocol uses a ticket-granting ticket (TGT) to authenticate users and grant access to network resources. When a user logs in to a domain, they receive a TGT from the domain controller. The TGT is used to request service tickets for specific network services.

When a user requests a service ticket, the Kerberos protocol generates a session key that is used to encrypt the communication between the user and the service. The session key is encrypted with the user's hashed password and included in the service ticket.

The Process of a Kerberoasting Attack

The attacker uses various tools and techniques to identify vulnerable user accounts in the AD domain that have SPNs associated with them. They then use a tool like Rubeus or Kekeo to request a service ticket for the targeted user account, which contains the user's password hash. They can then use a password cracking tool to obtain the plaintext password.

There are several ways to identify vulnerable user accounts in the AD domain. One method is to use a tool like BloodHound, which can map out the trust relationships between different domains and identify high-value targets. Another method is to use a tool like PowerView, which can search for user accounts with SPNs and extract information about their associated services.

Once the attacker has identified a vulnerable user account, they can use a tool like Rubeus or Kekeo to request a service ticket for the account. These tools can be used to request service tickets for multiple user accounts simultaneously, making the attack more efficient.

The attacker can then use a password cracking tool, such as Hashcat or John the Ripper, to crack the password hash and obtain the plaintext password. The plaintext password can then be used to gain access to sensitive information, such as confidential documents or financial data.

Detecting and Preventing Kerberoasting

Kerberoasting is a type of attack that targets the Kerberos authentication protocol, which is used to authenticate users and services in a Windows environment. The attack involves extracting the Kerberos service ticket for a user account that has a weak password, and then cracking the ticket to obtain the user's password hash. Once an attacker has the password hash, they can use it to gain unauthorized access to the user's account and sensitive data.

Common Signs of a Kerberoasting Attack

The signs of a Kerberoasting attack are not always obvious, but there are a few indicators that may help detect it. These include unusual service ticket requests, unauthorized access attempts, failed login attempts, and unusual network traffic patterns. For example, if an attacker is attempting to extract service tickets for multiple user accounts, there may be a spike in service ticket requests that is not typical for normal network activity. Similarly, if there are multiple failed login attempts for a single user account, it may be a sign that an attacker is attempting to guess the user's password.

It is important to note that these signs alone may not be sufficient to confirm a Kerberoasting attack, as they can also be caused by other factors. However, if these signs are noticed in conjunction with other suspicious activity, it may be worth investigating further.

Best Practices for Securing Kerberos

There are several best practices that can help secure the Kerberos authentication process. These include enforcing strong password policies, disabling unnecessary protocols and services, using encryption for network traffic, and regularly monitoring and auditing network activity.

Enforcing strong password policies can help prevent attackers from cracking passwords and gaining unauthorized access to user accounts. Password policies should require users to create complex, unique passwords that are changed regularly. Additionally, multi-factor authentication should be used to add an extra layer of security to the authentication process.

Disabling unnecessary protocols and services can help reduce the attack surface for Kerberoasting attacks. For example, the NTLM protocol should be disabled if it is not needed, as it is vulnerable to password cracking attacks.

Using encryption for network traffic can help prevent attackers from intercepting and eavesdropping on network traffic, which could be used to extract service tickets and password hashes. Kerberos can use encryption for authentication and service ticket exchange, which can be configured using Group Policy.

Regularly monitoring and auditing network activity can help detect and respond to Kerberoasting attacks in a timely manner. This can be done using monitoring and detection tools like the Windows Event Log and SIEM solutions, which can help identify abnormal behavior and patterns in network activity and trigger alerts for investigation and response.

Implementing Monitoring and Detection Tools

Organizations can use monitoring and detection tools like the Windows Event Log and SIEM solutions to detect and respond to Kerberoasting attacks. These tools can help identify abnormal behavior and patterns in network activity and trigger alerts for investigation and response.

The Windows Event Log can be used to monitor Kerberos authentication events, which can help detect Kerberoasting attacks. For example, failed service ticket requests or unusual service ticket requests may be signs of a Kerberoasting attack. SIEM solutions can be used to aggregate and correlate events from multiple sources, which can help identify patterns and anomalies that may be indicative of a Kerberoasting attack.

It is important to note that monitoring and detection tools are not foolproof, and may not detect all Kerberoasting attacks. However, they can provide valuable insight into network activity and help detect attacks in a timely manner, which can help minimize the impact of a successful attack.

Responding to a Kerberoasting Attack

Kerberoasting is a type of attack that targets the Kerberos authentication process used by Microsoft Active Directory. In this attack, an attacker can compromise a user account and extract the Kerberos ticket-granting ticket (TGT) that can be used to impersonate the user and gain access to sensitive resources. As Kerberoasting attacks can be difficult to detect, it is important to have a response plan in place to quickly identify and mitigate the attack.

Steps to Take After Discovering a Kerberoasting Attack

If a Kerberoasting attack is detected, a quick response is crucial to mitigate the damage and prevent further attacks. The first step is to disable the compromised user account to prevent the attacker from using it to access sensitive resources. Next, all passwords associated with the account should be changed to prevent the attacker from using any stolen credentials. It is also important to conduct a thorough investigation to determine the scope of the attack and identify any other compromised accounts or systems.

During the investigation, it may be necessary to review network logs to identify any suspicious activity or unusual network traffic. This can help to identify the source of the attack and any other compromised systems or accounts. It is also important to notify any affected users and stakeholders to keep them informed and to prevent any further damage.

Mitigating the Damage of a Kerberoasting Attack

After detecting a Kerberoasting attack, it is important to immediately take steps to mitigate the damage. This can include patching any vulnerabilities in the Kerberos authentication process to prevent further attacks. It may also be necessary to review and update security policies and procedures to prevent similar attacks from occurring in the future.

Another important step is to review and update password policies to ensure that they are strong and secure. This can include requiring longer and more complex passwords, implementing multi-factor authentication, and regularly changing passwords to prevent them from being compromised.

Strengthening Security Post-Attack

After a Kerberoasting attack, it is important to strengthen the security posture of the organization to prevent future attacks. This can include implementing additional security controls such as intrusion detection and prevention systems, network segmentation, and access controls to limit the scope of any future attacks.

Regular security awareness training for staff can also help to prevent future attacks by educating employees on how to identify and respond to potential threats. This can include training on how to identify phishing emails, how to create strong passwords, and how to report suspicious activity.

In conclusion, a quick and effective response to a Kerberoasting attack is crucial to mitigate the damage and prevent further attacks. By following these steps and implementing additional security measures, organizations can strengthen their security posture and reduce the risk of future attacks.