CVE-2021-38646 in Office
Summary
by MITRE • 09/15/2021
Microsoft Office Access Connectivity Engine Remote Code Execution Vulnerability
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Analysis
by VulDB Data Team • 05/03/2025
The Microsoft Office Access Connectivity Engine remote code execution vulnerability represents a critical security flaw that affects users of Microsoft Office applications and related database connectivity components. This vulnerability resides within the Access Connectivity Engine, a component that facilitates data access and manipulation for various Microsoft Office applications including Access, Excel, and other tools that rely on database connectivity. The flaw enables attackers to execute arbitrary code on vulnerable systems through specially crafted malicious files or data inputs that exploit the engine's processing mechanisms. According to the Common Weakness Enumeration catalog, this vulnerability maps to CWE-121, which describes heap-based buffer overflow conditions that occur when a program writes data beyond the boundaries of a fixed-length buffer. The vulnerability specifically impacts systems running Microsoft Office 2016, Office 2019, Office 2021, and Office 365 versions where the Access Connectivity Engine is installed and actively used for database operations.
The technical exploitation of this vulnerability occurs when the Access Connectivity Engine processes maliciously formatted data or files that trigger a buffer overflow condition in memory. Attackers can craft specially designed database files or data inputs that cause the engine to write beyond allocated memory boundaries, potentially leading to arbitrary code execution with the privileges of the user running the vulnerable application. This remote code execution capability allows threat actors to install malware, modify system files, access sensitive data, or establish persistent access to compromised systems. The vulnerability is particularly concerning because it can be triggered through legitimate Office application workflows when users open malicious files or connect to compromised data sources. The attack surface expands significantly when considering that many Office applications utilize the Access Connectivity Engine for data import operations, making it possible for attackers to exploit this vulnerability through various attack vectors including email attachments, web downloads, or compromised network shares.
The operational impact of CVE-2021-38646 extends beyond individual system compromise to potentially affect entire enterprise networks through lateral movement and privilege escalation attacks. Once an attacker gains initial access through this vulnerability, they can leverage the remote code execution capability to establish command and control channels, deploy additional malware payloads, or conduct reconnaissance activities against other network resources. This vulnerability aligns with several tactics described in the MITRE ATT&CK framework, particularly those related to execution, privilege escalation, and persistence. The vulnerability's exploitation typically follows the initial compromise phase where attackers use the remote code execution capability to gain a foothold, followed by privilege escalation techniques to obtain elevated system access. Organizations running affected Office versions are at heightened risk of targeted attacks, especially in environments where users frequently open email attachments or access external data sources through Office applications.
Mitigation strategies for this vulnerability require immediate patch management actions and comprehensive security configuration adjustments across affected systems. Microsoft released security updates that address this vulnerability through patches for the Access Connectivity Engine component, requiring administrators to deploy these updates promptly across all vulnerable systems. Organizations should implement network segmentation controls to limit access to systems that may be vulnerable, particularly those running older Office versions or applications that utilize the Access Connectivity Engine. Additional protective measures include enabling macro security settings in Office applications, implementing application whitelisting policies, and conducting regular security assessments to identify systems that may be running vulnerable components. Security teams should also monitor network traffic for suspicious activities that may indicate exploitation attempts and maintain updated threat intelligence feeds to understand emerging attack patterns targeting this specific vulnerability. The implementation of zero trust security models becomes particularly important when addressing vulnerabilities of this nature, as they require continuous verification of system integrity and user credentials throughout the attack lifecycle.