Windows Remote Desktop Protocol attacks are one of the most common ways cybercriminals gain access to business networks to install backdoors, gain access to sensitive data, and install ransomware and other forms of malware.

This attack method has been increasing in popularity over the past two years and there has also been a notable rise in darknet marketplaces selling exposed RDP services and RDP login credentials. The high number of Remote Desktop Protocol attacks has prompted the Federal Bureau of Investigation (FBI) Internet Crime Complaint Center (IC3) and the Department of Homeland Security to issue an alert to businesses in the United States to raise awareness of the threat.

Remote Desktop Protocol is a proprietary Windows network protocol that allows individuals to remotely access computers and servers over the Internet and gain full control of resources and data. RDP is often used for legitimate purposes, such as allowing managed security service providers (MSSPs) and managed service providers (MSPs) to remotely access devices to provide computer support without having to make a site visit. Through RDP, input such as mouse movements and keystrokes can be transmitted over the Internet with a graphical user interface sent back.

In order to gain access to a machine using RDP, a user must be authenticated by supplying a username and password. Once a user is authenticated, the resources on that device can be accessed. While authorized individuals can use RDP connections, so too can cybercriminals if they have access to login credentials or are able to guess usernames and passwords. As with any software, RDP can contain flaws. For instance, flaws in the CredSSP encryption mechanism could be exploited to perform man-in-the-middle attacks.

Cybercriminals are identifying vulnerable RDP sessions over the Internet and are exploiting them to gain access to sensitive information and conduct extortion attacks. The threat actors behind SamSam ransomware, which has been used in many attacks on U.S. businesses, educational institutions, and healthcare providers, often gain access to networks through brute force attempts to guess weak passwords. The threat actors behind CrySiS and CryptON ransomware attack businesses through open RDP ports and similarly use brute force and dictionary attacks to guess passwords.

How to Prevent Windows Remote Desktop Protocol Attacks

There are four main vulnerabilities that can be exploited to gain access to Windows devices that have RDP enabled:

  • Exploitation of weak passwords
  • Use of outdated versions of RDP
  • Failure to restrict access to the default RDP port – TCP 3389
  • Failure to block users after a set number of unsuccessful login attempts

Strong passwords should be used to make it harder for cybercriminals to use brute force tactics to guess login credentials. Dictionary words should be avoided. Default passwords must be changed and passwords should be at least 8 characters and include a mix of upper/lower case letters, numbers, and special characters. Rate limiting is also essential. A user should be blocked after a set number of failed login attempts have been made and, if possible, two-factor authentication controls should be implemented. External to internal RDP connections should be limited and software should be kept up to date.

An audit should be conducted to identify all systems that have RDP enabled, including cloud-based virtual machines with public IP addresses. If RDP is not required, it should be disabled. A list of systems with RDP enabled should be maintained and available patches should be applied promptly. All open RDP ports should be located behind a firewall and access should only be possible by using a VPN.

Logging mechanisms should be applied, and successful and unsuccessful login attempts should be regularly monitored to identify systems that have been attacked.

To ensure that recovery from a ransomware or sabotage attack is possible, all data must be regularly backed up and a good backup strategy adopted.

By regulating, monitoring, and controlling the use of RDP and addressing vulnerabilities, it is possible to reduce risk and prevent Remote Desktop Protocol attacks.