What is a Silver Ticket Attack and How to Prevent It?

What is a Silver Ticket Attack?

A silver ticket is a fake authentication ticket that is created when an attacker steals a user’s password from Active Directory (AD). This ticket is used to forge ticket-granting service tickets, allowing unauthorized access to targeted resources.

Silver ticket attacks exploit the Kerberos vulnerability, known as Kerberoasting, to harvest password hashes. Golden ticket and diamond ticket attacks also exploit this vulnerability, but silver tickets are more targeted in their use. If attackers gain access to your Active Directory via a silver ticket attack, they can bypass many cybersecurity measures.

Some ways to mitigate the damage of a silver ticket attack include enabling privileged attribute certificate validation of Kerberos, using a password service to create strong and random passwords, and restricting administrative privileges to prevent the attack from escalating.

How Does a Silver Ticket Attack Work?

The execution of a silver ticket attack requires the attacker to already have control of a compromised account within the AD environment. This initial compromise can occur through various forms of cyberattacks or malware. Once access is obtained, the attacker follows a step-by-step process to create forged authorization credentials. These steps are summarized below:

• Step 1: Gather information about the domain and the specific local service being targeted. This involves discovering the domain security identifier and the DNS name of the service.
• Step 2: Use a tool to acquire the local NTLM hash, or password hash, for the Kerberos service. The NTLM hash can be obtained from the local service account or security account manager of a compromised system.
• Step 3: Extract the unencrypted password from the NTLM hash using Kerberoasting.
• Step 4: Forge a Kerberos ticket granting service, which enables the attacker to authenticate to the desired target.
• Step 5: Use the forged tickets to achieve financial gain or further corrupt the system, depending on the attacker’s objective.

Once the attacker possesses the forged silver ticket, they can execute code on the targeted system. This allows them to elevate their privileges on the local host and begin moving laterally across the compromised environment, or even create a golden ticket.

Common Mitigation Strategies for Silver Ticket Attacks

To prevent credential dumping attacks like silver ticket attacks, there are several measures that can be taken. Firstly, it is important to prevent attackers from retrieving password information by securing access to it and limiting the access that a forged ticket can provide is crucial. To prevent successful Kerberoasting attacks, developers can encrypt data stored in memory and implement methods to regularly clear sensitive information, such as stored passwords. Auditing and strengthening service accounts can ensure that passwords are harder to discover and not shared across the network. Additionally, validating the Kerberos protocol is critical, ensuring that tickets were issued by the legitimate key distributor. To prevent silver ticket attacks, the following measures can be taken:

Educate users about password reuse and phishing attacks

Users should be trained to use unique passwords for each account and not to reuse passwords across different services. They should also be educated about how to identify and avoid phishing attacks, which are commonly used to harvest credentials for silver ticket attacks.

Manage a least-privilege model

Restricting user and domain administrator access to only the necessary privileges can limit the potential damage of a silver ticket attack. By granting users the minimum permissions required for their tasks, the attacker’s ability to escalate privileges and move laterally within the network is minimized.

Implement Kerberos with Privilege Attribute Certificate (PAC)

PAC allows for the inclusion of authorization data in the Kerberos tickets, enabling more secure authentication. Requiring the Ticket-Granting Service (TGS) to be signed by the Key Distribution Center (KDC) using the KRBTGT encryption key adds an additional layer of protection against forgery attacks.

Use strong, unique passwords for local user, administrator, and service accounts

One of the key components of silver ticket attacks is offline cracking of credentials. By ensuring that all local accounts have strong and unique passwords, the attacker’s ability to crack these credentials and generate fraudulent tickets is significantly diminished.

Implement tools to validate every ticket

It is important to have mechanisms in place that validate the authenticity of each ticket presented by a Kerberos principal (such as a service client). This involves collecting and validating all Kerberos authentication messages for each Service Principal Name (SPN) being protected. This helps to detect and reject any unauthorized or forged tickets.

Enable AES Kerberos encryption

It is recommended to use stronger encryption algorithms, such as AES, instead of weaker ones like RC4, wherever possible. This helps to enhance the security of the Kerberos authentication process, making it harder for attackers to manipulate or exploit the system.

How To Respond to A Silver Ticket Attack

After a silver ticket attack occurs, your cybersecurity team should respond immediately. This response should involve asking important questions and strengthening security measures based on the answers. These questions include determining how the attacker initially accessed the network, which accounts were targeted, what information they gained access to, and what assets have been compromised. Once the answers to these questions are known, the cybersecurity team can take countermeasures.

How Lepide Helps Protect Active Directory

The Lepide Data Security Platform can play a crucial role in preventing silver ticket attacks by actively monitoring and analyzing activities within Active Directory. It continuously monitors the Kerberos authentication process, enabling it to identify any unusual patterns or anomalies that may indicate a potential attack. For instance, it can quickly identify signs of Kerberos attacks, such as ticket reuse or manipulation of authentication tokens. Moreover, it can automatically detect and manage inactive service accounts, and detect and respond to failed login attempts in real-time. In the event of suspicious activity, the solution may notify the administrator or automatically execute a custom script to stop the potential attack in its tracks.

If you’d like to see how the Lepide Data Security Platform can help to safeguard your Active Directory, see our in-browser demo for Active Directory security.