CVE-2024-38016: Microsoft 365 Apps RCE Vulnerability

CVE-2024-38016 Overview

CVE-2024-38016 is a Remote Code Execution vulnerability affecting Microsoft Office Visio and related Microsoft 365 applications. This vulnerability allows attackers to execute arbitrary code on vulnerable systems when a user opens a specially crafted Visio file. The attack requires local access and user interaction, making it a prime candidate for social engineering attacks where malicious files are delivered via email or downloaded from untrusted sources.

Critical Impact

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code in the context of the current user, potentially leading to complete system compromise, data theft, or further lateral movement within an organization's network.

Affected Products

• Microsoft 365 Apps for Enterprise
• Microsoft Office 2019
• Microsoft Office Long Term Servicing Channel 2021
• Microsoft Visio 2016

Discovery Timeline

• September 19, 2024 - CVE-2024-38016 published to NVD
• September 24, 2024 - Last updated in NVD database

Technical Details for CVE-2024-38016

Vulnerability Analysis

This Remote Code Execution vulnerability in Microsoft Office Visio stems from improper access control (CWE-284) during the processing of Visio files. The vulnerability requires local access, meaning an attacker cannot directly exploit this over the network without first delivering a malicious file to the target system. User interaction is required - the victim must open a specially crafted Visio document for the attack to succeed.

Once triggered, the vulnerability allows the attacker to achieve code execution with the same privileges as the logged-in user. If the user has administrative privileges, the attacker could gain full control over the affected system, install programs, view/change/delete data, or create new accounts with full user rights.

Root Cause

The root cause of CVE-2024-38016 is identified as Improper Access Control (CWE-284). This classification indicates that the vulnerability exists due to insufficient restrictions on resource access within the Visio application. When processing certain file elements, the application fails to properly validate or restrict access to sensitive resources or operations, allowing an attacker to bypass intended security boundaries.

Attack Vector

The attack vector for CVE-2024-38016 is local, requiring the attacker to deliver a malicious Visio file to the victim. Common delivery mechanisms include:

• Phishing emails with malicious .vsdx or .vsd file attachments
• Hosting malicious Visio files on compromised or attacker-controlled websites
• Placing malicious files on network shares accessible to targeted users
• Social engineering users to download and open files from untrusted sources

The vulnerability requires no privileges to exploit but does require user interaction - specifically, the victim must open the malicious document. This makes it particularly dangerous in enterprise environments where Visio files are commonly shared for business workflows.

Detection Methods for CVE-2024-38016

Indicators of Compromise

• Unusual child processes spawned from visio.exe or Microsoft Office applications
• Unexpected network connections originating from Visio process
• Suspicious Visio files (.vsd, .vsdx, .vsdm) received via email from unknown senders
• Abnormal file system activity following the opening of Visio documents

Detection Strategies

• Monitor process execution chains for anomalous behavior stemming from visio.exe
• Implement email gateway rules to scan and quarantine suspicious Visio file attachments
• Deploy endpoint detection rules to identify code execution attempts from Office applications
• Enable Microsoft Defender Attack Surface Reduction (ASR) rules to block Office applications from creating child processes

Monitoring Recommendations

• Configure SIEM alerts for unusual Office application behavior patterns
• Enable enhanced logging for Microsoft Office applications via Windows Event Logs
• Monitor for process hollowing or injection techniques targeting Office processes
• Track file downloads and email attachments containing Visio file extensions

How to Mitigate CVE-2024-38016

Immediate Actions Required

• Apply the latest Microsoft security updates immediately for all affected products
• Educate users about the risks of opening Visio files from untrusted sources
• Consider blocking Visio file attachments at the email gateway until patches are applied
• Ensure Microsoft Defender or equivalent endpoint protection is enabled and updated

Patch Information

Microsoft has released security updates to address CVE-2024-38016. Detailed patch information and download links are available in the Microsoft Security Response Center Advisory. Organizations should prioritize patching the following products:

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

Workarounds

• Implement the principle of least privilege - ensure users operate with minimal necessary permissions
• Enable Protected View in Microsoft Office to open files from untrusted locations in read-only mode
• Configure Attack Surface Reduction rules in Microsoft Defender to restrict Office application behaviors
• Block or quarantine Visio file attachments from external email sources until systems are patched

# Enable Protected View for files from the Internet via Registry
reg add "HKCU\Software\Microsoft\Office\16.0\Visio\Security\ProtectedView" /v DisableInternetFilesInPV /t REG_DWORD /d 0 /f

# Enable Protected View for files in unsafe locations
reg add "HKCU\Software\Microsoft\Office\16.0\Visio\Security\ProtectedView" /v DisableUnsafeLocationsInPV /t REG_DWORD /d 0 /f