CVE-2023-36897: Microsoft 365 Apps Auth Bypass Vulnerability

CVE-2023-36897 Overview

CVE-2023-36897 is a spoofing vulnerability affecting the Visual Studio Tools for Office Runtime and related Microsoft products. This vulnerability stems from improper input validation (CWE-20), which could allow an attacker to deceive users or applications by spoofing trusted content or interfaces. The attack requires user interaction over a network vector, meaning a victim must be enticed to interact with malicious content for exploitation to succeed.

Critical Impact

Successful exploitation of this spoofing vulnerability could allow attackers to compromise the integrity of affected systems by impersonating trusted components or manipulating user interfaces, potentially leading to unauthorized actions or data manipulation.

Affected Products

• Microsoft 365 Apps (Enterprise, x64 and x86)
• Microsoft Office 2019 (x64 and x86)
• Microsoft Office 2021 LTSC (x64 and x86)
• Microsoft Visual Studio 2010 Tools for Office Runtime
• Microsoft Visual Studio 2017
• Microsoft Visual Studio 2019
• Microsoft Visual Studio 2022

Discovery Timeline

• August 8, 2023 - CVE-2023-36897 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-36897

Vulnerability Analysis

This spoofing vulnerability in Visual Studio Tools for Office Runtime allows an attacker to manipulate how trusted content or interfaces are presented to users. The vulnerability requires network access and user interaction to exploit, meaning an attacker cannot autonomously compromise a system—a victim must be convinced to interact with specially crafted malicious content.

The improper input validation weakness (CWE-20) indicates that the affected components fail to adequately verify or sanitize input data, creating an opportunity for attackers to inject spoofed content that appears legitimate. While this vulnerability does not directly enable code execution, successful exploitation could have high integrity impact, potentially allowing attackers to manipulate data or trick users into performing unintended actions.

Root Cause

The root cause of CVE-2023-36897 is improper input validation within the Visual Studio Tools for Office Runtime. The affected components do not properly validate certain inputs, allowing malicious actors to craft content that bypasses security controls designed to ensure authenticity and trustworthiness. This weakness in the validation logic creates an opportunity for spoofing attacks where untrusted content can masquerade as legitimate.

Attack Vector

The attack vector for this vulnerability is network-based and requires user interaction. An attacker would need to:

1. Craft malicious content designed to exploit the input validation weakness
2. Deliver this content to a victim through network-accessible means (such as email attachments, malicious websites, or shared documents)
3. Convince the victim to interact with the malicious content
4. Upon interaction, the spoofing attack succeeds, potentially misleading the user about the authenticity or origin of content

The vulnerability does not require elevated privileges to exploit, and the attack complexity is low once a victim can be enticed to interact with the malicious content. The primary impact is to integrity rather than confidentiality or availability.

Detection Methods for CVE-2023-36897

Indicators of Compromise

• Unexpected or suspicious Office documents or Visual Studio projects from untrusted sources
• Anomalous behavior in VSTO (Visual Studio Tools for Office) add-ins or runtime components
• User reports of content appearing legitimate but behaving unexpectedly
• Suspicious network activity associated with Office or Visual Studio applications

Detection Strategies

• Monitor for unusual VSTO runtime activity or add-in loading patterns
• Implement email security controls to detect and quarantine potentially malicious Office documents
• Deploy endpoint detection rules that alert on unexpected modifications to Office or Visual Studio configuration
• Review application logs for signs of spoofing attempts or abnormal component loading

Monitoring Recommendations

• Enable enhanced logging for Office applications and Visual Studio environments
• Monitor for attempts to load unsigned or untrusted VSTO add-ins
• Implement network monitoring to detect suspicious document downloads or sharing activity
• Configure SentinelOne Singularity Platform to detect behavioral anomalies in affected applications

How to Mitigate CVE-2023-36897

Immediate Actions Required

• Apply the security updates provided by Microsoft for all affected products immediately
• Ensure all instances of Visual Studio 2017, 2019, and 2022 are updated to patched versions
• Update Microsoft 365 Apps and Office installations to the latest security update
• Review and restrict VSTO add-in deployment policies within your organization

Patch Information

Microsoft has released security updates to address CVE-2023-36897. Detailed patch information and update guidance are available in the Microsoft Security Update Guide for CVE-2023-36897. Organizations should apply these updates through their standard patch management processes, prioritizing systems that actively use Visual Studio Tools for Office or VSTO-based solutions.

For Microsoft 365 Apps and Office products, ensure automatic updates are enabled or deploy updates through enterprise update channels. For Visual Studio installations, use the Visual Studio Installer to apply the latest security updates.

Workarounds

• Restrict execution of VSTO add-ins to only those from trusted publishers
• Implement strict macro and add-in policies in Office applications
• Educate users about the risks of interacting with untrusted documents or content
• Consider network segmentation to limit exposure of development environments
• Use application whitelisting to control which VSTO components can execute

# Example: PowerShell to check Visual Studio version for patch status
# Verify Visual Studio installations are updated
Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\VisualStudio\*\Setup\VS" -ErrorAction SilentlyContinue | Select-Object ProductDir, InstallDate

# Check Office update status via registry
Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\Office\ClickToRun\Configuration" -ErrorAction SilentlyContinue | Select-Object VersionToReport, UpdateChannel