CVE-2020-16896: Windows 10 RDP Information Disclosure Bug

CVE-2020-16896 Overview

An information disclosure vulnerability exists in the Windows Remote Desktop Protocol (RDP) implementation that allows attackers to obtain sensitive system information by connecting to vulnerable systems and sending specially crafted requests. This vulnerability affects a broad range of Microsoft Windows operating systems, including both client and server editions, making it a significant concern for enterprise environments where RDP is commonly used for remote administration.

The vulnerability occurs when the RDP service improperly handles certain connection requests, potentially leaking information that could be leveraged for further attacks against the compromised system. An attacker who successfully exploits this vulnerability could obtain sensitive data that may facilitate additional compromise of the target environment.

Critical Impact
Attackers can remotely extract sensitive system information via specially crafted RDP requests, potentially enabling follow-on attacks without requiring authentication or user interaction.

Affected Products

Microsoft Windows 10 (multiple versions including 1607, 1709, 1803, 1809, 1903, 1909, 2004)
Microsoft Windows 7 SP1 (x64 and x86)
Microsoft Windows 8.1 (x64 and x86)
Microsoft Windows RT 8.1
Microsoft Windows Server 2008 SP2 and R2 SP1
Microsoft Windows Server 2012 and R2
Microsoft Windows Server 2016 (including versions 1903, 1909, 2004)
Microsoft Windows Server 2019

Discovery Timeline

2020-10-16 - CVE-2020-16896 published to NVD
2026-02-23 - Last updated in NVD database

Technical Details for CVE-2020-16896

Vulnerability Analysis

This information disclosure vulnerability resides in the Remote Desktop Protocol implementation within Windows operating systems. The flaw allows network-based attackers to extract sensitive information from target systems without requiring any privileges or user interaction. The vulnerability is particularly concerning because RDP services are frequently exposed to external networks for remote administration purposes, expanding the potential attack surface significantly.

The exploitation mechanism involves sending malformed or specially crafted requests to the RDP service, which then improperly processes these requests and discloses information that should remain protected. This leaked information could include memory contents, configuration details, or other system data that attackers can use to plan and execute further attacks against the infrastructure.

Root Cause

The root cause stems from improper handling of connection requests by the Remote Desktop Protocol service. When processing certain types of RDP connection requests, the service fails to properly sanitize or validate the request contents, leading to unintended information exposure. Microsoft addressed this issue by correcting how RDP handles connection requests to prevent unauthorized information disclosure.

Attack Vector

The attack is conducted over the network by an adversary who connects to a vulnerable system's RDP service. The attacker sends specially crafted connection requests designed to trigger the information disclosure condition. This attack does not require authentication, user interaction, or special privileges, making it highly accessible to potential threat actors.

The attack flow typically involves:

Identifying systems with exposed RDP services (typically on TCP port 3389)
Establishing an RDP connection to the target system
Sending specially crafted requests that exploit the improper handling behavior
Receiving and parsing the disclosed information from the server response
Using gathered intelligence to plan subsequent attacks

Detection Methods for CVE-2020-16896

Indicators of Compromise

Unusual or malformed RDP connection attempts targeting TCP port 3389
Unexpected RDP connection patterns from external IP addresses
Anomalous network traffic volumes on RDP ports
RDP connection attempts with unusual request parameters or malformed protocol data

Detection Strategies

Monitor RDP connection logs for connections from suspicious or unknown IP addresses
Implement network intrusion detection rules to identify malformed RDP protocol messages
Enable Windows Security Event logging for Terminal Services connections (Event IDs 4624, 4625)
Deploy network traffic analysis to detect anomalous RDP traffic patterns

Monitoring Recommendations

Enable detailed logging on all systems running Remote Desktop Services
Centralize RDP authentication and connection logs to a SIEM platform for correlation
Monitor for reconnaissance activity targeting RDP services across the network
Implement alerting for RDP connections from geographic regions not aligned with normal business operations

How to Mitigate CVE-2020-16896

Immediate Actions Required

Apply Microsoft security updates immediately on all affected Windows systems
Restrict RDP access using Windows Firewall or network-level firewalls to trusted IP addresses only
Disable RDP on systems where remote desktop access is not required
Implement Network Level Authentication (NLA) to add an authentication layer before full RDP connections
Consider using VPN or Remote Desktop Gateway to limit direct RDP exposure to the internet

Patch Information

Microsoft has released security updates to address CVE-2020-16896 that correct how RDP handles connection requests. Organizations should apply the appropriate security updates for their specific Windows versions as detailed in the Microsoft Security Advisory. Given the network-accessible nature of this vulnerability and the high EPSS percentile indicating elevated exploitation probability, immediate patching is strongly recommended.

Workarounds

Block inbound RDP traffic (TCP 3389) at the network perimeter for systems not requiring external RDP access
Enable Network Level Authentication (NLA) to require authentication before establishing a full RDP session
Use Windows Firewall with Advanced Security to restrict RDP connections to specific trusted IP addresses
Deploy Remote Desktop Gateway to provide controlled and authenticated RDP access
Implement IP allowlisting for RDP access at the host firewall level

bash

# PowerShell: Enable Network Level Authentication (NLA) for RDP
Set-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp' -Name 'UserAuthentication' -Value 1

# PowerShell: Restrict RDP to specific IP addresses using Windows Firewall
New-NetFirewallRule -DisplayName "RDP Allow Trusted IPs" -Direction Inbound -Protocol TCP -LocalPort 3389 -RemoteAddress "10.0.0.0/8","192.168.1.0/24" -Action Allow
Set-NetFirewallRule -DisplayName "Remote Desktop - User Mode (TCP-In)" -Enabled False