CVE-2023-35336: Windows MSHTML Auth Bypass Vulnerability

CVE-2023-35336 Overview

CVE-2023-35336 is a security feature bypass vulnerability in the Windows MSHTML Platform, which is the rendering engine used by Internet Explorer and various other Windows components. This vulnerability allows attackers to bypass security features implemented in the MSHTML platform by exploiting improper input validation (CWE-20), potentially enabling malicious content to be processed or rendered in ways that circumvent intended security controls.

Critical Impact

This vulnerability could allow attackers to bypass security mechanisms in the Windows MSHTML Platform, potentially leading to integrity and availability impacts on affected systems when users interact with specially crafted content.

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

• July 11, 2023 - CVE-2023-35336 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-35336

Vulnerability Analysis

This security feature bypass vulnerability resides in the Windows MSHTML Platform, which serves as a critical component for rendering web content across multiple Windows applications. The vulnerability stems from improper input validation, allowing attackers to craft malicious content that bypasses security mechanisms designed to protect users from potentially harmful web-based attacks.

The MSHTML Platform is deeply integrated into Windows, being utilized not only by Internet Explorer but also by various applications that embed web content rendering capabilities. When security features within this platform are bypassed, it can potentially expose users to content that would normally be blocked or sanitized.

The vulnerability requires user interaction to exploit—typically through convincing a user to visit a malicious website or open a specially crafted document that leverages the MSHTML rendering engine. Upon successful exploitation, an attacker could potentially bypass security zones or other protective measures implemented by the platform.

Root Cause

The root cause of CVE-2023-35336 is improper input validation (CWE-20) within the Windows MSHTML Platform. The platform fails to properly validate certain inputs, which allows attackers to craft content that circumvents security feature checks. This validation gap enables malicious content to be processed in ways that should normally be prevented by the platform's security mechanisms.

Attack Vector

The attack vector for this vulnerability is network-based, meaning an attacker would typically need to host malicious content on a web server or deliver it through other network channels. Successful exploitation requires user interaction, such as:

1. Visiting a malicious website designed to exploit the vulnerability
2. Opening a specially crafted document that renders content through the MSHTML engine
3. Clicking on a malicious link delivered via email or other communication channels

The vulnerability allows attackers to bypass security features without requiring any privileges on the target system, though the impact is limited to low integrity and availability effects on the affected system.

Detection Methods for CVE-2023-35336

Indicators of Compromise

• Unusual process behavior involving mshtml.dll or Internet Explorer components loading unexpected content
• Web traffic to suspicious domains attempting to deliver crafted HTML content targeting MSHTML
• Unexpected network connections from applications that utilize the MSHTML rendering engine
• Log entries showing security zone bypass attempts or unusual content rendering patterns

Detection Strategies

• Monitor for anomalous behavior in processes that load mshtml.dll, particularly those attempting to access resources across security zones
• Implement web filtering to detect and block known malicious domains attempting to exploit MSHTML vulnerabilities
• Deploy endpoint detection rules to identify suspicious HTML content patterns associated with security feature bypass attempts
• Review application logs for warnings or errors related to MSHTML security feature processing

Monitoring Recommendations

• Enable detailed logging for Internet Explorer and MSHTML-related events in Windows Event Logs
• Configure network monitoring to detect unusual web content delivery patterns targeting Windows clients
• Implement behavioral monitoring on endpoints to detect applications exhibiting unexpected MSHTML rendering behavior
• Regularly review security zone configuration and ensure no unauthorized modifications have occurred

How to Mitigate CVE-2023-35336

Immediate Actions Required

• Apply the latest security updates from Microsoft that address CVE-2023-35336 immediately
• Ensure all affected Windows versions (Windows 10, Windows 11, Windows Server 2012 R2 through 2022) are updated
• Educate users about the risks of visiting untrusted websites or opening documents from unknown sources
• Consider implementing additional web filtering to block potentially malicious content

Patch Information

Microsoft has released security updates addressing CVE-2023-35336 as part of their July 2023 security update cycle. Organizations should apply the appropriate patches for their Windows versions by consulting the Microsoft Security Response Center advisory. The patches correct the improper input validation issue in the MSHTML Platform that allows the security feature bypass.

To verify the patch status, administrators can use Windows Update, Windows Server Update Services (WSUS), or Microsoft Endpoint Configuration Manager to ensure all systems have received the necessary security updates.

Workarounds

• Restrict access to Internet Explorer and applications that heavily rely on MSHTML rendering where possible
• Implement strict Group Policy settings to limit MSHTML functionality in high-security environments
• Consider using alternative browsers that do not rely on the MSHTML engine for web browsing activities
• Apply network segmentation to limit exposure of unpatched systems to potentially malicious web content

# Check Windows Update status for security patches
# Run in elevated PowerShell
Get-HotFix | Where-Object {$_.InstalledOn -gt (Get-Date).AddDays(-30)} | Format-Table -AutoSize

# Review installed updates related to MSHTML
wmic qfe list brief /format:table | findstr /i "KB"