CVE-2023-36413: Microsoft 365 Apps Auth Bypass Vulnerability

CVE-2023-36413 Overview

CVE-2023-36413 is a security feature bypass vulnerability affecting Microsoft Office products. This vulnerability allows attackers to circumvent security mechanisms designed to protect users from potentially malicious content. When successfully exploited, an attacker can bypass security features that would normally prevent the execution of untrusted content within Office documents, potentially allowing malicious payloads to execute without triggering expected security warnings.

Critical Impact

This security feature bypass vulnerability could allow attackers to deliver malicious Office documents that evade built-in security protections, potentially enabling social engineering attacks and malware delivery through seemingly legitimate document workflows.

Affected Products

• Microsoft 365 Apps (Enterprise)
• Microsoft Office 2016
• Microsoft Office 2019
• Microsoft Office Long Term Servicing Channel 2021

Discovery Timeline

• November 14, 2023 - CVE-2023-36413 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-36413

Vulnerability Analysis

This vulnerability represents a security feature bypass in Microsoft Office applications. The attack requires user interaction, specifically requiring a user to open a specially crafted file. The vulnerability allows an attacker to bypass security features that are intended to protect users from malicious content embedded within Office documents.

The bypass can result in high integrity impact, meaning attackers can modify protected data or system resources that should otherwise be safeguarded by Office's security mechanisms. This type of vulnerability is particularly dangerous in enterprise environments where Office documents are routinely shared and trusted by users.

Root Cause

The root cause of CVE-2023-36413 involves improper security feature implementation within Microsoft Office. The vulnerability exists due to insufficient enforcement of security controls that are designed to prevent untrusted or potentially malicious content from executing within Office applications. This allows specially crafted documents to bypass protections that users rely upon for safe document handling.

Attack Vector

The attack vector is network-based, requiring an attacker to deliver a malicious Office document to the victim. The attack complexity is low, meaning no special conditions need to be met beyond convincing a user to open the crafted document. Successful exploitation requires user interaction—specifically, the victim must open the malicious file.

Common delivery methods for this type of attack include:

• Phishing emails with malicious Office document attachments
• Compromised websites hosting weaponized documents
• File sharing platforms distributing infected files
• Social engineering attacks targeting specific individuals

The vulnerability affects document integrity, allowing attackers to bypass security features without impacting confidentiality or availability directly.

Detection Methods for CVE-2023-36413

Indicators of Compromise

• Unusual Office document behavior where security warnings that should appear are bypassed
• Office documents received from untrusted sources exhibiting unexpected functionality
• Endpoint detection alerts related to Office applications performing anomalous actions

Detection Strategies

• Monitor for Office applications spawning unexpected child processes after opening documents
• Implement email gateway scanning to detect potentially malicious Office document attachments
• Deploy endpoint detection solutions capable of identifying security feature bypass attempts
• Enable Microsoft Defender for Office 365 to scan documents for malicious content

Monitoring Recommendations

• Enable detailed logging for Microsoft Office applications to track document-related events
• Configure SIEM rules to alert on Office applications exhibiting unusual process behaviors
• Monitor network traffic for suspicious document downloads from untrusted sources
• Implement user and entity behavior analytics to detect anomalous document access patterns

How to Mitigate CVE-2023-36413

Immediate Actions Required

• Apply the Microsoft security update addressing CVE-2023-36413 immediately
• Educate users about the risks of opening Office documents from untrusted sources
• Enable Protected View for all Office applications to add an additional layer of security
• Review and strengthen email filtering rules to quarantine suspicious Office attachments

Patch Information

Microsoft has released a security update to address this vulnerability. Organizations should apply the patch available through Microsoft Security Update Guide. The update is available through standard Microsoft Update channels including Windows Update, WSUS, and Microsoft Update Catalog.

Affected versions requiring updates:

• Microsoft 365 Apps for Enterprise
• Microsoft Office 2016
• Microsoft Office 2019
• Microsoft Office LTSC 2021

Workarounds

• Configure Microsoft Office to open documents from the internet in Protected View by default
• Implement strict email attachment policies blocking Office documents with macros or active content
• Use application whitelisting to control which Office documents can execute content
• Consider deploying Office documents through secure, vetted channels only until patching is complete

# Registry configuration to enforce Protected View for Office files from the internet
# This adds an additional layer of protection for untrusted documents
reg add "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableInternetFilesInPV /t REG_DWORD /d 0 /f
reg add "HKCU\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView" /v DisableInternetFilesInPV /t REG_DWORD /d 0 /f
reg add "HKCU\Software\Microsoft\Office\16.0\PowerPoint\Security\ProtectedView" /v DisableInternetFilesInPV /t REG_DWORD /d 0 /f