Guarding the Gates: Understanding and Mitigating RDP Brute Force Attacks

Introduction: The Digital Doorway

Remote Desktop Protocol (RDP) has become an indispensable tool for many organizations, allowing employees to access their work computers or servers from anywhere in the world. However, like any doorway, if not properly secured, it can become an entry point for unwanted guests. Enter the world of RDP brute force attacks.

What is an RDP Brute Force Attack?

An RDP brute force attack is a type of cyberattack where attackers attempt to gain unauthorized access to a system by guessing the credentials (username and password) of its RDP account. Using automated tools, attackers can make thousands of login attempts in a short period, cycling through various combinations of usernames and passwords until they find a match.

Why RDP?

1. Ubiquity: RDP is widely used across industries, making it a common target.
2. Direct Access: Successful RDP attacks grant direct access to a system, bypassing many security layers.
3. Lack of Monitoring: Many organizations don’t monitor RDP access as closely as they should, allowing attackers to operate undetected.

Technical Deep Dive: How It Works

1. Reconnaissance: Finding the Open Doors
   • Before launching an attack, cybercriminals first need to identify their targets. This involves scanning vast IP ranges to detect systems with open RDP ports (typically TCP 3389).
   • Tools in Action:
     • Shodan: Often dubbed the “search engine for open ports,” Shodan allows attackers to find devices with specific open ports, including RDP.
     • masscan: This is the fastest Internet port scanner. It can scan the entire Internet in under 6 minutes, transmitting 10 million packets per second.
2. Launching the Attack: Automated Barrage
   • Once potential targets are identified, attackers deploy automated tools to initiate a barrage of login attempts. These tools can process vast lists of commonly used credentials, attempting thousands of combinations in quick succession.
   • Tools in Action:
     • Hydra: A parallelized login cracker that supports numerous protocols, including RDP. It’s renowned for its speed and versatility.
     • Ncrack: Developed by the Nmap project, Ncrack is a high-speed network authentication cracking tool designed to help experts secure their networks.
3. Gaining Entry: Exploiting Human Tendencies
   • Attackers often capitalize on human tendencies, such as using weak or default passwords. Commonly used passwords like “password123” or “admin” are usually the first to be tried.
   • Credential Stuffing: This is a type of cyberattack where known username-password pairs are used to gain unauthorized access. Given the number of data breaches, vast lists of known credentials are available on the dark web.
4. Ensuring Return: Creating Backdoors
   • Once inside, attackers don’t just rely on the credentials they’ve cracked. They often create backdoors or deploy malware to ensure they can return to the compromised system, even if the original credentials are changed or the breach is detected.
   • Shadow Admins: Attackers might create hidden admin accounts, granting them full control over the system without the knowledge of the system’s owner.
   • RAT Deployment: Remote Access Trojans (RATs) can be installed to provide attackers with a stealthy backdoor into the system, often undetected by conventional antivirus solutions.
5. Expanding the Attack Surface: Lateral Movement
   • Once inside a network, attackers often don’t stay put. They use the compromised system as a launchpad, moving laterally across the network, seeking more valuable data or systems.
   • Pass-the-Hash: This technique allows attackers to authenticate as a user without knowing their plaintext password. Instead, they use the NTLM hash of the user’s password to spawn new sessions, further infiltrating the network.
   • Mimikatz: A post-exploitation tool that’s used to extract credentials from memory. It’s particularly effective in environments where users have logged into multiple systems, as it can retrieve plaintext passwords, hashes, and Kerberos tickets.

The Consequences

1. Data Theft: Unauthorized RDP access can lead to sensitive data being stolen.
2. Ransomware: RDP breaches are a common initial step in ransomware attacks.
3. System Manipulation: Attackers can install malicious software, delete data, or even use the compromised system as a launchpad for attacks on other systems.

Guarding Against RDP Brute Force Attacks

1. Strong Passwords: Ensure all RDP accounts use complex, unique passwords.
2. Account Lockouts: Implement account lockout policies after a certain number of failed login attempts.
3. Two-Factor Authentication (2FA): Add an extra layer of security by requiring a second form of authentication.
4. Network Level Authentication (NLA): This requires users to authenticate before a full RDP session is established.
5. RDP Gateways: Use an RDP gateway to hide the actual RDP server and add an additional layer of authentication.
6. Regular Monitoring: Regularly review RDP logs to detect and respond to suspicious activity.
7. Limit Exposure: If possible, avoid exposing RDP to the internet. Use VPNs or other secure methods to access RDP sessions.

Conclusion

While RDP offers unparalleled convenience for remote access, it’s crucial to understand the risks associated with it. By implementing robust security measures and staying informed about potential threats, organizations can enjoy the benefits of RDP without leaving their systems vulnerable to brute force attacks.