CVE-2024-42220: Microsoft Outlook Auth Bypass Vulnerability

CVE-2024-42220 Overview

A library injection vulnerability exists in Microsoft Outlook 16.83.3 for macOS that allows attackers to leverage Outlook's access privileges, leading to a permission bypass. A specially crafted library can be injected by a malicious application, which then starts the program to trigger this vulnerability and abuse the vulnerable application's permissions. This vulnerability falls under the category of DLL Injection/Process Injection vulnerabilities.

Critical Impact

A malicious application could inject a library into Microsoft Outlook for macOS, bypassing permission controls and gaining access to sensitive user data, calendar information, and email communications with elevated privileges.

Affected Products

• Microsoft Outlook 16.83.3 for macOS
• macOS systems running vulnerable versions of Microsoft Outlook

Discovery Timeline

• 2024-12-18 - CVE-2024-42220 published to NVD
• 2025-08-22 - Last updated in NVD database

Technical Details for CVE-2024-42220

Vulnerability Analysis

This vulnerability is classified under CWE-347 (Improper Verification of Cryptographic Signature), indicating that Microsoft Outlook for macOS fails to properly verify the cryptographic signatures of libraries before loading them. This allows an attacker with local access to craft a malicious library that can be injected into the Outlook process.

The vulnerability enables attackers to bypass macOS permission controls that normally protect user data. When Outlook loads an untrusted library, that library inherits all of Outlook's granted permissions, including access to contacts, calendars, emails, and potentially other sensitive system resources that the user has previously authorized Outlook to access.

Root Cause

The root cause of this vulnerability lies in insufficient validation of library signatures before dynamic loading. Microsoft Outlook for macOS does not adequately verify that libraries being loaded are properly signed and trusted, allowing malicious code to be executed within the context of the Outlook application. This represents a failure in the application's security architecture to enforce code signing requirements on dynamically loaded components.

Attack Vector

The attack requires a malicious application to be present on the target macOS system. The attacker would craft a specially designed library that exploits Outlook's library loading mechanism. When the malicious application injects this library and triggers Outlook to load it, the injected code executes with Outlook's full permission set. This can include access to the user's email, contacts, calendar, and any other resources that Outlook has been granted access to through macOS privacy permissions.

The network attack vector classification indicates that the malicious library or application could be delivered remotely, though local execution is required for the injection to occur. The attack does not require user interaction beyond the initial compromise that places the malicious application on the system.

Detection Methods for CVE-2024-42220

Indicators of Compromise

• Unexpected libraries loaded by the Microsoft Outlook process that are not signed by Microsoft
• Unusual file system activity in Outlook's application bundle or library paths
• Anomalous network connections originating from the Outlook process to unknown destinations
• Modified or newly created library files in system or user library directories that interact with Outlook

Detection Strategies

• Monitor for unsigned or improperly signed libraries being loaded by Microsoft Outlook using macOS code signing verification tools
• Implement endpoint detection rules to alert on library injection attempts targeting Microsoft applications
• Use file integrity monitoring to detect unauthorized modifications to Outlook's application bundle or associated libraries
• Deploy behavioral analysis to identify processes attempting to inject code into Microsoft Outlook

Monitoring Recommendations

• Enable detailed process logging on macOS endpoints to capture library loading events
• Configure SentinelOne agents to monitor for suspicious library injection patterns and code signing violations
• Review macOS Console logs for any library loading errors or security violations related to Microsoft Outlook
• Implement application allowlisting to prevent unauthorized applications from running that could perform injection attacks

How to Mitigate CVE-2024-42220

Immediate Actions Required

• Update Microsoft Outlook for macOS to the latest available version from Microsoft
• Audit macOS systems for any signs of compromise or unauthorized applications
• Review and restrict application permissions in macOS System Settings > Privacy & Security
• Ensure Gatekeeper and code signing enforcement are enabled on all macOS endpoints

Patch Information

Microsoft has acknowledged this vulnerability. Organizations should update Microsoft Outlook for macOS to the latest version available through Microsoft AutoUpdate or the Mac App Store. For detailed vulnerability information, refer to the Talos Intelligence Vulnerability Report.

Workarounds

• Restrict which applications can interact with Microsoft Outlook using macOS application firewall and privacy controls
• Implement application control policies to prevent unauthorized applications from executing on corporate macOS devices
• Enable System Integrity Protection (SIP) and ensure it is not disabled on managed endpoints
• Consider using Microsoft Defender for Endpoint or SentinelOne to provide additional runtime protection against library injection attacks
• Limit user privileges to reduce the impact of a potential compromise

# Verify Microsoft Outlook code signature integrity on macOS
codesign --verify --deep --strict /Applications/Microsoft\ Outlook.app

# Check for any unsigned libraries loaded by Outlook
sudo fs_usage -f filesystem Microsoft\ Outlook 2>&1 | grep -i dylib

# Enable enhanced security logging
log config --mode "level:debug" --subsystem com.apple.security