CVE-2021-41368: Microsoft Access RCE Vulnerability

CVE-2021-41368 Overview

CVE-2021-41368 is a Remote Code Execution (RCE) vulnerability affecting Microsoft Access, a component included in various Microsoft Office product suites. This vulnerability allows an attacker to execute arbitrary code on a target system when a user opens a specially crafted Microsoft Access file. The attack requires user interaction, as the victim must open a malicious file for the exploit to succeed.

Critical Impact

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

Affected Products

• Microsoft 365 Apps for Enterprise
• Microsoft Office 2013 SP1, 2016, and 2019
• Microsoft Office Long Term Servicing Channel 2021

Discovery Timeline

• 2021-11-10 - CVE-2021-41368 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-41368

Vulnerability Analysis

This vulnerability exists within Microsoft Access, allowing remote code execution through specially crafted files. The attack vector is local, meaning an attacker must convince a user to open a malicious file—typically delivered through phishing campaigns, malicious email attachments, or compromised downloads.

According to the Zero Day Initiative Advisory ZDI-21-1309, this vulnerability was coordinated through their disclosure program. The local attack vector combined with no required privileges but mandatory user interaction indicates a social engineering component to successful exploitation.

The vulnerability affects multiple versions of Microsoft Office spanning several years of releases, from Office 2013 SP1 through the Long Term Servicing Channel 2021, creating a broad attack surface across enterprise and consumer environments.

Root Cause

Microsoft has not disclosed specific technical details about the root cause of this vulnerability. The CWE classification indicates insufficient information is available to categorize the exact weakness type. However, the Remote Code Execution nature suggests potential issues with improper handling of file contents, memory corruption, or insufficient input validation within Microsoft Access file parsing routines.

Attack Vector

The attack vector for CVE-2021-41368 requires local access, meaning the attacker must deliver the malicious file to the target system and convince the user to open it. Common delivery methods include:

The vulnerability manifests when Microsoft Access processes a specially crafted file. Upon opening such a file, the vulnerable component fails to properly validate or handle certain data structures, allowing an attacker to execute arbitrary code in the context of the current user. If the user has administrative privileges, the attacker could gain complete control over the affected system.

For technical implementation details, refer to the Microsoft Security Advisory CVE-2021-41368.

Detection Methods for CVE-2021-41368

Indicators of Compromise

• Unexpected Microsoft Access files (.accdb, .mdb) received via email or downloaded from untrusted sources
• Microsoft Access crashing or behaving unexpectedly after opening files
• Unusual child processes spawned by MSACCESS.EXE
• Suspicious network connections originating from Office application processes

Detection Strategies

• Monitor for MSACCESS.EXE spawning unexpected child processes such as cmd.exe, powershell.exe, or script interpreters
• Implement file scanning for malicious Access database files at email gateways and endpoints
• Use SentinelOne's behavioral AI to detect anomalous process execution patterns associated with Office application exploitation
• Enable Microsoft Office Protected View and monitor for bypass attempts

Monitoring Recommendations

• Configure endpoint detection solutions to alert on suspicious process genealogy from Office applications
• Implement logging for file access events involving Access database files from external sources
• Monitor for Office application processes making unusual network connections
• Review security logs for evidence of exploitation attempts during patch gap periods

How to Mitigate CVE-2021-41368

Immediate Actions Required

• Apply the latest Microsoft security updates for all affected Office products immediately
• Enable Microsoft Office Protected View to open files from untrusted locations in read-only mode
• Educate users about the risks of opening Access files from unknown or untrusted sources
• Consider blocking Access database file types at the email gateway if not required for business operations

Patch Information

Microsoft has released security patches addressing this vulnerability as part of their November 2021 security updates. Organizations should apply the appropriate patches for their Office installations:

• Microsoft 365 Apps: Update to the latest version through Microsoft Update
• Microsoft Office 2013 SP1, 2016, 2019: Apply the November 2021 cumulative updates
• Microsoft Office LTSC 2021: Update to the latest patched version

Detailed patch information is available in the Microsoft Security Advisory CVE-2021-41368.

Workarounds

• Enable Protected View for files originating from the internet in Microsoft Office Trust Center settings
• Configure Application Guard for Office to isolate potentially malicious documents
• Restrict Microsoft Access file associations for users who do not require Access functionality
• Implement email filtering rules to quarantine or block Access database file attachments

# PowerShell: Check installed Office version and update status
Get-ItemProperty HKLM:\SOFTWARE\Microsoft\Office\ClickToRun\Configuration | Select-Object -Property VersionToReport, UpdateChannel, Platform

# Force Office update check
"C:\Program Files\Common Files\Microsoft Shared\ClickToRun\OfficeC2RClient.exe" /update user