CVE-2023-36762: Microsoft Word RCE Vulnerability

CVE-2023-36762 Overview

CVE-2023-36762 is a Remote Code Execution (RCE) vulnerability affecting Microsoft Word and related Microsoft Office products. This vulnerability allows attackers to execute arbitrary code on a victim's system when a user opens a specially crafted Word document. The attack requires local access and user interaction, meaning successful exploitation depends on convincing a user to open a malicious document.

Critical Impact

Successful exploitation of this vulnerability enables attackers to execute arbitrary code with the privileges of the current user, potentially leading to complete system compromise, data theft, or further lateral movement within an organization.

Affected Products

• Microsoft 365 Apps for Enterprise (x64 and x86)
• Microsoft Office 2019 (Windows x64/x86 and macOS)
• Microsoft Office Long Term Servicing Channel 2021 (Windows x64/x86 and macOS)
• Microsoft SharePoint Server 2016 Enterprise
• Microsoft Word 2016 (x64 and x86)

Discovery Timeline

• September 12, 2023 - CVE-2023-36762 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-36762

Vulnerability Analysis

This Remote Code Execution vulnerability in Microsoft Word stems from improper input validation (CWE-20) when processing specially crafted documents. The vulnerability exists in how Microsoft Word handles certain document elements, allowing an attacker to craft a malicious document that, when opened by a victim, triggers the execution of arbitrary code.

The attack requires local access to the target system and depends on user interaction—specifically, the victim must open a malicious Word document. Once opened, the vulnerability can be exploited to execute code in the context of the current user. If the user has administrative privileges, an attacker could gain full control over the affected system, install programs, view or modify data, or create new accounts with full user rights.

Root Cause

The root cause of CVE-2023-36762 is improper input validation (CWE-20) within Microsoft Word's document parsing functionality. When processing certain document structures or embedded content, Word fails to properly validate or sanitize input, creating an opportunity for attackers to inject and execute malicious code. This type of vulnerability is common in complex document processing applications that must handle various file formats, embedded objects, and rich content.

Attack Vector

The attack vector for this vulnerability is local, requiring an attacker to deliver a malicious Word document to the victim. Common delivery methods include:

• Phishing emails with malicious Word document attachments
• Social engineering to trick users into downloading documents from compromised websites
• Placing malicious documents on network shares or collaboration platforms

Once the victim opens the document, the malicious payload executes without any additional user interaction beyond the initial file open operation. The Preview Pane in Windows Explorer may also trigger the vulnerability when previewing malicious files.

The vulnerability mechanism involves crafting document content that exploits the input validation flaw in Word's document parser. For detailed technical information, refer to the Microsoft Security Advisory.

Detection Methods for CVE-2023-36762

Indicators of Compromise

• Unexpected Word process (WINWORD.EXE) spawning child processes, particularly command interpreters like cmd.exe or powershell.exe
• Unusual network connections originating from Microsoft Word processes
• Word documents with suspicious or obfuscated embedded content received via email or downloaded from untrusted sources
• Abnormal memory allocation patterns or crashes in Word processes

Detection Strategies

• Deploy endpoint detection and response (EDR) solutions to monitor for suspicious process chains involving Microsoft Word
• Configure email security gateways to scan and sandbox Word document attachments before delivery
• Implement application control policies to restrict Word from executing unexpected child processes
• Enable Windows Defender Exploit Guard to detect and block exploitation attempts

Monitoring Recommendations

• Monitor Windows Event Logs for process creation events (Event ID 4688) where WINWORD.EXE is the parent process
• Track file system activity for Word documents being opened from temporary directories or uncommon locations
• Set up alerts for Office applications attempting to load unsigned or suspicious DLLs
• Implement network monitoring to detect unusual outbound connections from Office processes

How to Mitigate CVE-2023-36762

Immediate Actions Required

• Apply the latest Microsoft security updates for all affected Office products immediately
• Enable Protected View in Microsoft Word to restrict document functionality until explicitly trusted
• Block execution of Office macros and active content from untrusted sources
• Educate users about the risks of opening Word documents from unknown or suspicious sources

Patch Information

Microsoft has released security patches addressing CVE-2023-36762 as part of the September 2023 Patch Tuesday updates. Organizations should apply the appropriate updates for their installed Office products through Windows Update, Microsoft Update, or WSUS. Detailed patch information and download links are available in the Microsoft Security Response Center Advisory.

Affected product versions include:

• Microsoft 365 Apps for Enterprise
• Microsoft Office 2019 (Windows and macOS)
• Microsoft Office LTSC 2021 (Windows and macOS)
• Microsoft SharePoint Server 2016
• Microsoft Word 2016

Workarounds

• Enable Protected View for files originating from the Internet by navigating to File > Options > Trust Center > Trust Center Settings > Protected View
• Configure Microsoft Office to block Active-X controls and macros in documents from untrusted locations
• Use Application Guard for Office (if available) to open untrusted documents in an isolated container
• Implement email attachment filtering to quarantine or block Word documents from external senders

# Registry configuration to enforce Protected View settings
# Enable Protected View for files from the Internet
reg add "HKCU\Software\Microsoft\Office\16.0\Word\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\Word\Security\ProtectedView" /v DisableUnsafeLocationsInPV /t REG_DWORD /d 0 /f

# Enable Protected View for Outlook attachments
reg add "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableAttachmentsInPV /t REG_DWORD /d 0 /f