What is a Kerberoasting Attack and How to Prevent It

  • By Greg Brown
  • May 08, 2023

What is a Kerberoasting Attack

A lot of us are fascinated with technology. Any form or mention of the subject piques an interest or at least a glance of curiosity. Unfortunately, we must endure the dark side of technology as well. 

From the beginning of the computer age, there have always been hackers who could match their criminal expertise to current technologies. Some hackers are concerned with small scams and easy entry points. Dangerous and brilliant predators plan their attacks down to the millisecond, along with specific goals for the attack. These types of hackers are extremely valuable on the world stage.

What is a Kerberoasting Attack?

The same hierarchy exists in every hacking group on the planet, those criminals wanting only the easy score and the brainy attackers looking to make a statement on the most complex systems.

Hackers with the smarts to carry out a successful Kerberoasting attack know the complexity of the Windows Server environment and its multiple subsystems. Kerberoasting attacks were discovered in 2014 by Tim Medin, CEO of Red Siege Information Security. Tim wrote a paper in 2015 on “how to attack Kerberoasting. “Kicking the Guard Dog of Hades”

“Kerberoasting is a post-exploitation technique that attempts to steal a password hash from an Active Directory account on a Windows server. The attack explicitly targets an account with a Service Principal Name or SPN.

Hackers specifically target the Kerberos database, which stores passwords and other personally identifiable information inside the server system. 

The Kerberoasting attack begins when an authenticated domain user requests a Kerberoasting ticket for an SPN.” 

In somewhat simpler terms, the SPN directive combines a service name with a computer and user account; giving it a unique identifier. Supposition says within the inner workings of the Windows server, there exists a unique number that matches user accounts with a tunnel to the outside.

How Hackers Use Kerberoasting Attack?

  • “Enumerate service principal names,” target service accounts
  • Request TGS tickets 
  • Crack the Passwords offline using a password spraying attack
  • Use the new privileges that were just stolen 

How to Spot Kerberoasting Attack?

  1. Kerberos Authentication
  2. Post-Exploitation
  3. Active Directory and SPN

1 - Kerberos Authentication

Kerberos is a computer network authentication protocol. The Kerberos protocol communicates from network node to node with tickets. Nodes are the endpoints in the network, such as your computer, printer, or anything connected to the flow of information. 

The client-server authentication model stipulates that all data exchange is encrypted, including passwords.

Kerberos authentication uses symmetric key cryptography inside the server environment to authenticate user identities within an Active Directory environment. Kerberos involves three basic tenets; 1) A ticket-granting server, 2) Kerberos database, 3) Authentication.

Network admins use Kerberos as an authentication method for several reasons, such as access control and security. 

2 - Post-Exploitation

Post-Exploitation is a phase of the Kerberoasting attack that creates a set of rules and techniques to determine the value of a compromised machine and maintain its control for later use. The phase is a vulnerability scan, a single section of the entire security framework organizations must take for an effective security protocol

The post-exploitation phase contains the hackers technique of where to proceed after entry has been made. Post-exploitation is a single step in a chain of events for the brilliant hacker. Once an attack has started and depending on the rules of the attack, the hack may never use a post-exploitation phase. However, if the phase is used, it is considered an extension of tactics and techniques used in previous server attacks.

  • Situation awareness
  • Reliable re-entry
  • Attain privilege escalation
  • Harvest credentials to move laterally through the network.

Once installed, post-exploitation maintains access to a compromised machine and the escalation privileges on that system. The phase allows hackers to stay connected to a machine and return later to achieve another attack goal.

3 - Active Directory and SPN

In a Windows Server environment, Active Directories is a multi-layer database that stores the information or objects on the network. Active directories make this information available to network admins and users at a later date. Hierarchies and storing data on active directories is a topic for a later date. 

The Service Principal Name or SPN associates a unique identifier (a combination of numbers and characters) to every server process or instance; admins then can go to a specific identifier number and correct critical errors. Once the hacker requests a Kerberos ticket for an SPN, they can identify the specific account with the encrypted password.

Hackers collect all that is collectible and go offline. With a Kerberoasting attack, getting offline is vital and gives attackers the time to get every piece of information needed to use ransomware and other money extraction methods to their fullest. 

It may take a matter of a few minutes, days, or even months to crack the encrypted database. As a last resort, attackers may use a brute force attack method on the files to uncover the passwords. 

A brute force attack attempts to overwhelm the target with wave after wave of faulty computer keys, malware code, and malicious algorithms to get the info needed.

The cyber attack has yielded a trove of password files and other account information. If the attackers are looking, they may focus on upper-level management and the decision-makers. These are the people who will pay anything to get their company back or keep private information private.

To Wrap Up

In the world of hacking, there is usually a specific target when a complex hack such as a Kerberoasting comes into play. For elite hackers to get into the target system, perform the hack, and get out, specific risk and exposure factors must happen.

Elite hacking groups around the world on some of the most dangerous this planet holds. Their ability to hack into any computer, server, or network is frightening. In 2022 alone, ransomware netted elite hackers over $70 million. 

A good hack is getting into a system, getting out, and never being discovered, which is sometimes the point of the hack.

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