CVE-2024-21307: Windows 10 1507 RCE Vulnerability

CVE-2024-21307 Overview

CVE-2024-21307 is a Remote Code Execution (RCE) vulnerability affecting the Microsoft Remote Desktop Client across a wide range of Windows operating systems. This vulnerability stems from use-after-free (CWE-416) and race condition (CWE-362) weaknesses in the Remote Desktop Client component. An attacker who successfully exploits this vulnerability could execute arbitrary code on the target system with the privileges of the user running the Remote Desktop Client.

Critical Impact

Successful exploitation allows attackers to achieve remote code execution on vulnerable Windows systems when users connect to malicious RDP servers, potentially leading to complete system compromise.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1809, 21H2, 22H2)
• Microsoft Windows 11 (versions 21H2, 22H2, 23H2)
• Microsoft Windows Server 2008 R2 SP1, 2012, 2012 R2, 2016, 2019, 2022

Discovery Timeline

• January 9, 2024 - CVE-2024-21307 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2024-21307

Vulnerability Analysis

This vulnerability exists within the Microsoft Remote Desktop Client (mstsc.exe) and involves a combination of use-after-free (UAF) and race condition flaws. The vulnerability requires an attacker to set up a malicious RDP server and convince a user to connect to it. While the attack requires user interaction and has a high complexity due to the race condition timing requirements, successful exploitation can result in complete compromise of confidentiality, integrity, and availability of the affected system.

The vulnerability is network-accessible but requires high attack complexity due to the inherent race condition timing constraints. No privileges are required on the attacker's side, but user interaction is necessary to establish the malicious connection.

Root Cause

The root cause involves two interrelated weaknesses:

1. Use-After-Free (CWE-416): The Remote Desktop Client improperly handles memory during RDP session processing, allowing access to memory after it has been freed. This can lead to memory corruption and arbitrary code execution.

2. Race Condition (CWE-362): A timing vulnerability exists where concurrent operations can lead to an inconsistent state, enabling exploitation of the use-after-free condition. The attacker must win a race condition to successfully trigger the vulnerability.

Attack Vector

The attack vector is network-based and follows this general exploitation path:

1. The attacker sets up a malicious RDP server configured to exploit the vulnerability
2. The victim is socially engineered to connect their Remote Desktop Client to the attacker-controlled server
3. During the RDP handshake or session, the malicious server sends specially crafted data
4. The crafted data triggers the race condition in the Remote Desktop Client
5. If timing conditions are met, the use-after-free vulnerability is exploited
6. Arbitrary code executes with the privileges of the user running the Remote Desktop Client

The vulnerability manifests during RDP session handling when the client processes server-side responses. Technical exploitation details can be found in the Microsoft Security Advisory.

Detection Methods for CVE-2024-21307

Indicators of Compromise

• Unexpected outbound RDP connections to unknown or suspicious IP addresses
• Crashes or abnormal behavior of mstsc.exe (Remote Desktop Client)
• Memory access violations in Remote Desktop Client processes
• Unusual network traffic patterns during RDP sessions

Detection Strategies

• Monitor for RDP client connections to untrusted or external hosts using network traffic analysis
• Implement endpoint detection rules for abnormal Remote Desktop Client behavior or crashes
• Deploy behavioral analysis to detect exploitation attempts targeting memory corruption in RDP components
• Review Windows Event Logs for RDP client connection events to unfamiliar destinations

Monitoring Recommendations

• Enable verbose logging for Remote Desktop Client connections
• Configure SIEM alerts for RDP connections to IP addresses outside approved ranges
• Monitor process creation and memory access patterns for mstsc.exe
• Implement network segmentation monitoring for outbound RDP traffic

How to Mitigate CVE-2024-21307

Immediate Actions Required

• Apply Microsoft's January 2024 security updates immediately across all affected Windows systems
• Restrict RDP client usage to connect only to known, trusted RDP servers
• Implement network policies to limit outbound RDP connections to approved destinations
• Educate users about the risks of connecting to unknown or untrusted RDP servers

Patch Information

Microsoft has released security updates addressing this vulnerability as part of the January 2024 Patch Tuesday release cycle. Detailed patch information and download links are available in the Microsoft Security Update Guide for CVE-2024-21307. Organizations should prioritize patching based on the criticality of affected systems and their exposure to potential attack scenarios.

Workarounds

• Implement firewall rules to block outbound RDP connections to untrusted networks
• Use Network Level Authentication (NLA) for all RDP connections where possible
• Deploy application control policies to restrict Remote Desktop Client execution to authorized users only
• Consider using VPN or secure tunnels for all remote desktop connectivity to reduce attack surface

# Configuration example - Block outbound RDP to untrusted networks via Windows Firewall
netsh advfirewall firewall add rule name="Block Outbound RDP" dir=out action=block protocol=tcp remoteport=3389 enable=yes

# Allow outbound RDP only to trusted corporate RDP servers
netsh advfirewall firewall add rule name="Allow RDP to Trusted Servers" dir=out action=allow protocol=tcp remoteip=10.0.0.0/8,192.168.1.0/24 remoteport=3389 enable=yes