CVE-2023-35332: Windows 10 1507 RDP Auth Bypass Flaw

CVE-2023-35332 Overview

CVE-2023-35332 is a security feature bypass vulnerability affecting the Windows Remote Desktop Protocol (RDP). This vulnerability relates to inadequate cryptographic strength (CWE-326) in the RDP implementation, potentially allowing attackers to bypass security features designed to protect remote desktop connections. The vulnerability requires network access and user interaction to exploit, making it a targeted attack vector for sophisticated threat actors seeking to compromise Windows systems through RDP.

Critical Impact

Successful exploitation could allow attackers to bypass RDP security features, potentially compromising the confidentiality and integrity of remote desktop sessions across a wide range of Windows client and server systems.

Affected Products

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

Discovery Timeline

• 2023-07-11 - CVE-2023-35332 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-35332

Vulnerability Analysis

This vulnerability stems from inadequate cryptographic strength in the Windows Remote Desktop Protocol implementation. The weakness allows an attacker positioned on the network to potentially bypass security mechanisms that protect RDP sessions. Exploitation requires user interaction, indicating that social engineering or other techniques may be necessary to successfully trigger the vulnerability.

The vulnerability affects the security features designed to protect the integrity and confidentiality of RDP communications. When exploited, an attacker could potentially intercept or manipulate RDP session data, though availability of the system is not impacted.

Root Cause

The root cause is classified as CWE-326: Inadequate Encryption Strength. This indicates that the RDP implementation uses cryptographic mechanisms that do not provide sufficient protection against modern attack techniques. The weak encryption allows security features to be circumvented under certain conditions, particularly when an attacker can position themselves between the client and server.

Attack Vector

The attack vector is network-based, meaning an attacker must have network access to the target system. However, the attack complexity is high, requiring specific conditions to be met for successful exploitation. User interaction is required, suggesting that the victim must perform some action (such as connecting to a malicious RDP server or accepting a compromised connection) for the attack to succeed.

The vulnerability could potentially be exploited through man-in-the-middle positioning where an attacker intercepts RDP traffic, or by convincing a user to connect to a malicious RDP endpoint that exploits the weak cryptographic implementation.

Detection Methods for CVE-2023-35332

Indicators of Compromise

• Unusual RDP connection attempts from unexpected source IP addresses
• RDP sessions established with non-standard or weakened encryption parameters
• Network traffic anomalies indicating potential man-in-the-middle positioning on RDP ports (TCP 3389)

Detection Strategies

• Monitor Windows Event Logs for RDP connection events (Event IDs 1149, 4624, 4625) with unusual characteristics
• Implement network monitoring to detect RDP traffic patterns that deviate from established baselines
• Deploy endpoint detection to identify attempts to exploit RDP security feature bypass vulnerabilities
• Audit RDP security settings to ensure strong encryption is enforced across the environment

Monitoring Recommendations

• Enable enhanced logging for Remote Desktop Services and Terminal Services
• Implement network segmentation monitoring to detect lateral movement attempts via RDP
• Configure alerting for RDP connections from untrusted networks or geographical locations
• Review Group Policy settings for RDP encryption requirements regularly

How to Mitigate CVE-2023-35332

Immediate Actions Required

• Apply the security updates from Microsoft's July 2023 Patch Tuesday release immediately
• Restrict RDP access to only necessary systems and users using Windows Firewall or network-level controls
• Implement Network Level Authentication (NLA) for all RDP connections
• Consider using a VPN or Remote Desktop Gateway to add additional layers of security for RDP access

Patch Information

Microsoft has released security updates to address this vulnerability as part of the July 2023 security updates. Administrators should consult the Microsoft Security Update Guide for specific KB articles and patch details for each affected Windows version. Updates are available through Windows Update, Windows Server Update Services (WSUS), and the Microsoft Update Catalog.

Workarounds

• Disable RDP on systems where remote desktop access is not required
• Implement strict firewall rules to limit RDP access to specific trusted IP addresses only
• Use jump servers or bastion hosts to consolidate and monitor RDP access points
• Enable RDP connection auditing and regularly review access logs for suspicious activity

# PowerShell: Verify RDP encryption level and NLA settings
Get-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp' -Name 'MinEncryptionLevel'
Get-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp' -Name 'UserAuthentication'

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