CVE-2024-26199: Microsoft 365 Apps Privilege Escalation

CVE-2024-26199 Overview

CVE-2024-26199 is an Elevation of Privilege vulnerability affecting Microsoft Office products. This vulnerability allows a local attacker with low privileges to escalate their permissions on the affected system. The flaw is associated with CWE-59 (Improper Link Resolution Before File Access, commonly known as a Symlink Attack), indicating that the vulnerability involves improper handling of symbolic links or file system references within Microsoft Office components.

Critical Impact

A local attacker with low-privilege access can exploit this vulnerability to gain elevated privileges on the system, potentially achieving complete control over confidentiality, integrity, and availability of the affected system.

Affected Products

• Microsoft 365 Apps (Enterprise, x64)
• Microsoft 365 Apps (all editions)
• Microsoft Office components using 365 Apps platform

Discovery Timeline

• 2024-03-12 - CVE-2024-26199 published to NVD
• 2024-12-06 - Last updated in NVD database

Technical Details for CVE-2024-26199

Vulnerability Analysis

This elevation of privilege vulnerability exists due to improper link resolution before file access (CWE-59) within Microsoft Office components. The vulnerability requires local access to the system and low-privilege user credentials to exploit. Once exploited, an attacker can achieve high impact across all three security pillars: confidentiality, integrity, and availability.

The local attack vector combined with low attack complexity and no user interaction requirement makes this vulnerability particularly concerning for enterprise environments where multiple users share access to systems running Microsoft 365 Apps.

Root Cause

The root cause of CVE-2024-26199 stems from improper link resolution before file access, classified under CWE-59 (Symlink Attack). This type of vulnerability typically occurs when an application follows symbolic links or junctions without properly validating the destination path, allowing an attacker to redirect file operations to privileged locations or resources.

In the context of Microsoft Office, this could involve manipulating file system links to trick Office components into performing operations with elevated privileges, such as writing to protected directories or accessing sensitive files that the attacker would not normally have permission to access.

Attack Vector

The attack vector for CVE-2024-26199 is local, meaning an attacker must have initial access to the target system. The exploitation scenario typically involves:

1. An attacker gains low-privilege access to a system running Microsoft 365 Apps
2. The attacker creates malicious symbolic links or file system junctions targeting privileged resources
3. When Microsoft Office components interact with these manipulated paths, they follow the links without proper validation
4. The attacker leverages this behavior to perform privileged operations, effectively escalating their access level on the system

Since no user interaction is required, the exploitation can occur during normal Office operations without alerting the user.

Detection Methods for CVE-2024-26199

Indicators of Compromise

• Suspicious symbolic link creation in Office-related directories or temporary folders
• Unusual file system activity from Office processes accessing privileged system paths
• Unexpected modifications to protected files or directories by Office applications
• Process creation anomalies where Office components spawn unexpected child processes with elevated privileges

Detection Strategies

• Monitor for symlink and junction creation events in directories commonly accessed by Microsoft Office applications
• Implement file integrity monitoring on critical system directories to detect unauthorized modifications
• Use endpoint detection and response (EDR) solutions to track privilege escalation attempts originating from Office processes
• Enable Windows Security Event logging for file system operations and analyze for suspicious patterns

Monitoring Recommendations

• Configure SentinelOne to monitor for abnormal process behavior from Microsoft Office applications
• Enable detailed logging for file system operations involving symbolic links and junctions
• Set up alerts for Office processes attempting to access or modify files outside their expected operational scope
• Implement behavioral analysis rules to detect privilege escalation patterns from low-privilege users

How to Mitigate CVE-2024-26199

Immediate Actions Required

• Apply the latest security updates from Microsoft for all Microsoft 365 Apps installations
• Review and audit user permissions on systems running Microsoft Office to ensure principle of least privilege
• Enable Windows Defender Exploit Guard and Attack Surface Reduction rules for Office applications
• Consider restricting symbolic link creation capabilities for non-administrative users where operationally feasible

Patch Information

Microsoft has released security updates to address CVE-2024-26199. Organizations should apply the patches available through Windows Update or Microsoft Update Catalog. For detailed patch information and affected versions, refer to the Microsoft Security Response Center Advisory.

Enterprise environments using Microsoft 365 Apps should ensure automatic updates are enabled or deploy patches through their software management systems such as Microsoft Endpoint Configuration Manager (MECM) or Intune.

Workarounds

• If immediate patching is not possible, consider restricting user access to systems with Microsoft Office installations
• Implement additional monitoring and alerting for file system operations involving symbolic links
• Use Windows Group Policy to limit symbolic link creation (SeCreateSymbolicLinkPrivilege) for standard users
• Isolate high-value systems from users who do not require Microsoft Office functionality until patches can be applied

# Check for Microsoft 365 Apps update status via PowerShell
# Run as administrator to verify installed Office version
Get-ItemProperty HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\* | 
  Where-Object { $_.DisplayName -like "*Microsoft 365*" } | 
  Select-Object DisplayName, DisplayVersion, InstallDate

# Force Office update check
& "C:\Program Files\Common Files\microsoft shared\ClickToRun\OfficeC2RClient.exe" /update user