A remote code execution vulnerability exists in Remote Desktop Services – formerly known as Terminal Services – when an unauthenticated attacker connects to the target system using RDP and sends specially crafted requests. This vulnerability is pre-authentication and requires no user interaction. An attacker who successfully exploited this vulnerability could execute arbitrary code on the target system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.
To exploit this vulnerability, an attacker would need to send a specially crafted request to the target systems Remote Desktop Service via RDP.
The update addresses the vulnerability by correcting how Remote Desktop Services handles connection requests.
The following workaround may be helpful in your situation. In all cases, Microsoft strongly recommends that you install the updates for this vulnerability as soon as possible even if you plan to leave these workarounds in place:
1. Enable Network Level Authentication (NLA)
You can enable Network Level Authentication to block unauthenticated attackers from exploiting this vulnerability. With NLA turned on, an attacker would first need to authenticate to Remote Desktop Services using a valid account on the target system before the attacker could exploit the vulnerability.
2. Block TCP port 3389 at the enterprise perimeter firewall
TCP port 3389 is used to initiate a connection with the affected component. Blocking this port at the network perimeter firewall will help protect systems that are behind that firewall from attempts to exploit this vulnerability. This can help protect networks from attacks that originate outside the enterprise perimeter. Blocking the affected ports at the enterprise perimeter is the best defense to help avoid Internet-based attacks. However, systems could still be vulnerable to attacks from within their enterprise perimeter.
The following mitigation may be helpful in your situation. In all cases, Microsoft strongly recommends that you install the updates for this vulnerability as soon as possible even if you plan to leave Remote Desktop Services disabled:
1. Disable Remote Desktop Services if they are not required.
If you no longer need these services on your system, consider disabling them as a security best practice. Disabling unused and unneeded services helps reduce your exposure to security vulnerabilities.