CVE-2023-36805: Windows MSHTML Auth Bypass Vulnerability

CVE-2023-36805 Overview

CVE-2023-36805 is a security feature bypass vulnerability affecting the Windows MSHTML Platform, the core rendering engine used by Internet Explorer and legacy web content in Windows. This vulnerability allows attackers to bypass security protections implemented in the MSHTML platform, potentially enabling the execution of malicious content that would otherwise be blocked by Windows security mechanisms.

The MSHTML platform remains a critical component in Windows systems as it handles rendering of web content in various applications beyond just Internet Explorer, including Microsoft Office documents with embedded web content and other legacy applications.

Critical Impact

Successful exploitation of this vulnerability could allow attackers to bypass security features designed to protect users from malicious web content, potentially leading to arbitrary code execution on affected systems.

Affected Products

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

Discovery Timeline

• September 12, 2023 - CVE-2023-36805 published to NVD
• April 8, 2025 - Last updated in NVD database

Technical Details for CVE-2023-36805

Vulnerability Analysis

This security feature bypass vulnerability exists in the Windows MSHTML Platform, which is responsible for rendering HTML content and executing scripts in Internet Explorer and legacy applications. The vulnerability is classified under CWE-77 (Command Injection), indicating that the flaw may allow attackers to inject and execute commands by circumventing security controls.

The attack requires local access to the target system and user interaction, meaning an attacker would need to convince a user to open a specially crafted file or visit a malicious website. Despite these prerequisites, successful exploitation can result in high impact to confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of CVE-2023-36805 lies in improper validation or enforcement of security features within the MSHTML rendering engine. The platform fails to adequately enforce security boundaries in certain scenarios, allowing specially crafted content to bypass protections that would normally prevent execution of potentially malicious code or commands.

Attack Vector

The vulnerability requires a local attack vector with high complexity. An attacker must craft malicious content specifically designed to exploit the security feature bypass. The attack chain typically involves:

1. The attacker creates a specially crafted document or web content that exploits the MSHTML security bypass
2. The victim must be convinced to open the malicious content (requiring user interaction)
3. Upon opening, the MSHTML platform processes the content and fails to properly enforce security restrictions
4. The attacker's payload bypasses security features, potentially leading to command execution with the privileges of the current user

The vulnerability mechanism exploits weaknesses in how the MSHTML platform validates and enforces security policies. Technical details regarding the specific bypass technique can be found in the Microsoft Security Update Guide.

Detection Methods for CVE-2023-36805

Indicators of Compromise

• Unusual mshta.exe process spawning or executing unexpected commands
• Internet Explorer or MSHTML-based applications accessing suspicious URLs or local files
• Anomalous child processes spawned from iexplore.exe or applications using the MSHTML engine
• Registry modifications related to Internet Explorer or MSHTML security settings

Detection Strategies

• Monitor process creation events for mshta.exe with unusual command-line arguments
• Implement behavioral detection for MSHTML-based applications spawning unexpected child processes
• Deploy endpoint detection rules to identify attempts to bypass Internet Explorer security zones
• Analyze network traffic for connections initiated by legacy IE components to untrusted destinations

Monitoring Recommendations

• Enable Windows Event logging for process creation (Event ID 4688) with command-line auditing
• Configure SentinelOne Singularity Platform to monitor MSHTML-related process activity and behavioral anomalies
• Implement file integrity monitoring for critical MSHTML-related system files
• Review application logs for errors or warnings related to security zone violations

How to Mitigate CVE-2023-36805

Immediate Actions Required

• Apply Microsoft's security updates for September 2023 Patch Tuesday immediately
• Review and restrict the use of Internet Explorer and MSHTML-based applications where possible
• Educate users about the risks of opening untrusted documents or clicking suspicious links
• Enable Protected Mode and Enhanced Protected Mode in Internet Explorer if still in use

Patch Information

Microsoft has released security updates addressing CVE-2023-36805 as part of their September 2023 security update cycle. Administrators should consult the Microsoft Security Update Guide for CVE-2023-36805 for specific patch information and KB article numbers for each affected product.

Organizations should prioritize patching based on their exposure to MSHTML-based content and the criticality of affected systems. Windows Update, Windows Server Update Services (WSUS), or Microsoft Endpoint Configuration Manager can be used to deploy the patches.

Workarounds

• Restrict or disable Internet Explorer and MSHTML-based applications where feasible
• Implement application allowlisting to prevent unauthorized execution of mshta.exe
• Configure Group Policy to enforce strict Internet Explorer security zone settings
• Deploy network-level filtering to block access to known malicious content sources

# Restrict mshta.exe execution via Windows Defender Application Control
# Add to WDAC policy file to block mshta.exe
# Create a deny rule for mshta.exe in your organization's WDAC policy

# Alternative: Use Group Policy to restrict MSHTML
# Navigate to: Computer Configuration > Administrative Templates > Windows Components > Internet Explorer
# Enable "Turn off the Security Settings Check feature" and configure security zones appropriately