CVE-2025-29966: Microsoft Remote Desktop RCE Vulnerability

CVE-2025-29966 Overview

CVE-2025-29966 is a heap-based buffer overflow vulnerability affecting Microsoft Windows Remote Desktop that enables unauthorized attackers to execute arbitrary code over a network. This vulnerability exists in the Remote Desktop Protocol (RDP) client implementation and can be triggered when a user connects to a malicious RDP server. The flaw allows attackers to corrupt heap memory, potentially leading to full system compromise without requiring authentication.

Critical Impact

This vulnerability enables remote code execution through the Windows Remote Desktop client, potentially allowing attackers to gain complete control of affected systems when users connect to malicious RDP servers.

Affected Products

• Microsoft Remote Desktop Client
• Microsoft Windows App
• Microsoft Windows 10 (versions 1507, 1607, 1809, 21H2, 22H2)
• Microsoft Windows 11 (versions 22H2, 23H2, 24H2)
• Microsoft Windows Server 2008 R2 SP1
• Microsoft Windows Server 2012 and 2012 R2
• Microsoft Windows Server 2016, 2019, 2022, 2022 23H2, and 2025

Discovery Timeline

• May 13, 2025 - CVE-2025-29966 published to NVD
• May 19, 2025 - Last updated in NVD database

Technical Details for CVE-2025-29966

Vulnerability Analysis

This vulnerability is classified under CWE-122 (Heap-based Buffer Overflow) and CWE-787 (Out-of-bounds Write). The flaw resides in the Windows Remote Desktop client's handling of certain data structures during RDP session negotiation or data processing. When a user connects to a malicious RDP server, specially crafted responses can trigger the heap buffer overflow condition.

The vulnerability requires user interaction, specifically requiring a victim to initiate a Remote Desktop connection to an attacker-controlled server. However, no prior authentication is required from the attacker's perspective, making this vulnerability particularly dangerous in scenarios where users may be tricked into connecting to malicious RDP endpoints through phishing or other social engineering techniques.

Root Cause

The root cause stems from improper bounds checking in the Remote Desktop client when processing server responses. The application fails to properly validate the size of incoming data before writing it to a heap-allocated buffer, allowing an attacker to overflow the buffer boundaries. This out-of-bounds write condition can corrupt adjacent heap metadata or application data, enabling arbitrary code execution.

Attack Vector

The attack is network-based and requires user interaction. An attacker would typically:

1. Set up a malicious RDP server configured to send crafted responses
2. Lure a victim to connect to the malicious server through phishing emails, malicious links, or compromised legitimate services
3. When the victim's Remote Desktop client connects, the server sends specially crafted data that triggers the heap overflow
4. The overflow corrupts heap memory, allowing the attacker to execute arbitrary code in the context of the user running the RDP client

The attack does not require any privileges on the victim's system, and exploitation can lead to complete system compromise with the privileges of the user running the Remote Desktop client.

Detection Methods for CVE-2025-29966

Indicators of Compromise

• Unusual Remote Desktop client crashes or unexpected terminations during connection attempts
• Connections to suspicious or unknown RDP server addresses in network logs
• Unexpected child processes spawned by mstsc.exe or Remote Desktop client applications
• Memory access violations or heap corruption errors in Windows Event Logs related to RDP components

Detection Strategies

• Monitor for anomalous RDP client behavior including unexpected crashes or high memory consumption
• Implement network monitoring to detect connections to known malicious or suspicious RDP endpoints
• Deploy endpoint detection rules to identify exploitation attempts targeting heap overflow conditions in RDP clients
• Review application crash dumps for signs of heap corruption in Remote Desktop-related processes

Monitoring Recommendations

• Enable Windows Event Log collection for Application and System logs, filtering for Remote Desktop client events
• Configure network security tools to log and alert on outbound RDP connections (TCP 3389) to non-approved destinations
• Implement SentinelOne's real-time monitoring capabilities to detect memory corruption exploitation attempts
• Establish baseline RDP connection patterns and alert on deviations indicating potential malicious activity

How to Mitigate CVE-2025-29966

Immediate Actions Required

• Apply Microsoft security updates immediately for all affected Windows versions and Remote Desktop clients
• Restrict Remote Desktop client usage to trusted, approved RDP servers only
• Educate users about the risks of connecting to untrusted RDP endpoints and recognizing phishing attempts
• Consider blocking outbound RDP connections at the network perimeter except to known-good destinations

Patch Information

Microsoft has released security updates addressing this vulnerability. Detailed patch information is available through the Microsoft Security Response Center advisory for CVE-2025-29966. Organizations should prioritize applying these updates across all affected systems, including both Windows operating systems and standalone Remote Desktop client applications.

Workarounds

• Implement strict network controls limiting RDP client connections to pre-approved, trusted servers
• Use Remote Desktop Gateway servers with certificate validation to prevent connections to arbitrary endpoints
• Deploy application whitelisting to control which applications can initiate outbound network connections
• Consider using alternative remote access solutions with additional security controls until patches are applied

# Block outbound RDP connections except to trusted servers using Windows Firewall
# Run in PowerShell as Administrator

# First, block all outbound RDP by default
New-NetFirewallRule -DisplayName "Block Outbound RDP" -Direction Outbound -LocalPort 3389 -Protocol TCP -Action Block

# Then, allow connections only to trusted RDP servers (replace with your approved server IPs)
New-NetFirewallRule -DisplayName "Allow RDP to Trusted Server" -Direction Outbound -LocalPort 3389 -Protocol TCP -RemoteAddress "192.168.1.100" -Action Allow