As red team members and pen testers, we are often tasked with testing the security of a target’s Remote Desktop Protocol (RDP) service. Pass-the-hash (PTH) is a technique commonly used by attackers to gain access to a system through stolen credentials. In this article, we will explore using the xfreerdp tool to connect to an RDP server using PTH techniques.

What is Pass-the-Hash?

Pass-the-Hash is a technique for authenticating to a system using the hash of a user’s password instead of the actual password. The hash is obtained by stealing the password hash from the target system. This technique is commonly used by attackers who have already compromised a system and have access to the password hashes.

When a user logs into a Windows system, the password is hashed and stored in memory as a hash value. This hash value is then used to authenticate the user for subsequent logins. Attackers can obtain the password hash through various techniques, such as using Mimikatz or other similar tools. Once the hash value is obtained, it can authenticate to the system as the user without needing the actual password.

Using Pass-the-Hash to Connect to an RDP Server

Now that we understand Pass-the-Hash, let’s explore using this technique to connect to an RDP server using xfreerdp. Xfreerdp is an open-source RDP client that supports Pass-the-Hash authentication.

First, we need to obtain a user’s password hash to access the target RDP server. We can use Mimikatz or similar tools to extract the password hash. Once we have the password hash, we can use xfreerdp to connect to the RDP server.

Here’s an example command to connect to an RDP server using xfreerdp with Pass-the-Hash authentication:

xfreerdp /v:<target_ip> /u:<username> /pth:<hash_value>

Let’s break down this command:

  • /v:<target_ip> specifies the IP address of the target RDP server.
  • /u:<username> specifies the username of the user whose password hash we obtained.
  • /pth:<hash_value> specifies the password hash value obtained using Mimikatz or other similar tools.

Once we execute this command, xfreerdp will attempt to authenticate to the RDP server using the password hash. We will be connected to the RDP server as the specified user if successful.

Here’s an example command using xfreerdp to connect to an RDP server with Pass-the-Hash authentication:

xfreerdp /v:192.168.1.10 /u:admin /pth:7b455e245e1c7f1d2c3a7d305ba65f22

In this example, we are attempting to connect to an RDP server with the IP address 192.168.1.10 using the username “admin” and the password hash “7b455e245e1c7f1d2c3a7d305ba65f22”.

Limitations of Pass-the-Hash

While Pass-the-Hash can be an effective technique for gaining access to a system, this approach has some limitations. One of the main limitations is that Pass-the-Hash only works if the user whose password hash was stolen has access to the system. If the user does not have access, then this technique will not work.

Another limitation is that Pass-the-Hash only works for authentication purposes. Once authenticated, the attacker still needs to escalate their privileges to gain further access to the system. This can be achieved through privilege escalation techniques, such as exploiting vulnerabilities or using other methods to obtain higher-level access.

Additionally, some security tools can detect pass-the-hash attacks. For example, Microsoft’s Enhanced Mitigation Experience Toolkit (EMET) can detect them and prevent them from succeeding. Other security tools, such as intrusion detection systems (IDS), can also detect them and alert security teams.

Therefore, it’s essential to understand Pass-the-Hash’s limitations and use it in combination with other techniques to achieve our goals as red team members and pen testers.

Real-World Examples

Pass-the-hash has been used in various real-world attacks. One example is the Target breach in 2013, where attackers used stolen credentials to access the Target network and steal customer data. The attackers used a combination of techniques, including Pass-the-Hash, to gain access to the network and move laterally to steal the data.

Another example is the 2014 Sony Pictures hack, in which attackers used stolen credentials and Pass-the-Hash to gain access to the network and steal sensitive data. They also used other techniques, such as malware and social engineering, to access the network.

Conclusion

Pass-the-hash is a powerful technique that can be used to gain access to a system using stolen credentials. As red team members and pen testers, it’s essential to understand this technique and how to use it effectively. Xfreerdp is a valuable tool for connecting to an RDP server using Pass-the-Hash authentication. However, it’s essential to understand Pass-the-Hash’s limitations and use it in combination with other techniques to achieve our goals. By understanding Pass-the-Hash and using it effectively, we can improve our red teaming and pen testing skills and help improve the overall security of our organizations.