KB5002839 — Security Update for Microsoft Word 2016

Overview

KB5002839 is a critical security update released on February 10, 2026, for Microsoft Word 2016 and Outlook 2016. This update addresses multiple high-severity vulnerabilities that could allow remote code execution and information disclosure attacks. The update applies to both 32-bit and 64-bit editions of these Office applications and is essential for maintaining security in enterprise and personal computing environments.

Security Vulnerabilities Addressed

This security update resolves several critical vulnerabilities in Microsoft Office 2016 components:

Remote Code Execution Vulnerabilities

The primary security concern addressed by KB5002839 involves remote code execution flaws in the Office document parsing engine. These vulnerabilities could allow attackers to execute arbitrary code by convincing users to open specially crafted Word documents or Outlook email attachments. The vulnerabilities affect the core document processing components and could be exploited without user interaction beyond opening a malicious file.

Information Disclosure Issues

The update also patches information disclosure vulnerabilities that could allow attackers to read sensitive data from application memory. These flaws could expose cached credentials, email content, or other confidential information stored in memory during normal Office operations.

Memory Corruption Flaws

Several memory corruption vulnerabilities are addressed, particularly in font rendering and embedded object processing. These flaws could lead to application crashes or, in worst-case scenarios, code execution when processing malicious content.

Affected Systems and Components

This security update applies to the following Microsoft Office 2016 applications and components:

Installation Requirements and Process

The installation process for KB5002839 varies depending on your Office 2016 deployment method:

Click-to-Run Installations

For most consumer and small business installations using Click-to-Run technology, the update is delivered automatically through the Office update mechanism. Users can manually trigger updates by opening any Office application and navigating to the Account section.

Volume License Installations

Enterprise customers with volume license agreements can obtain the update through traditional deployment channels including WSUS, SCCM, and direct download from the Microsoft Update Catalog.

System Requirements

Before installing this update, verify that your system meets the following requirements:

• Supported Windows operating system (Windows 7 SP1 or later)
• Microsoft Office 2016 with minimum version 16.0.4266.1001
• Sufficient disk space for temporary installation files
• Administrative privileges for MSI-based installations

Security Impact and Risk Assessment

The vulnerabilities addressed by KB5002839 are classified as critical due to their potential for remote code execution without user interaction beyond opening a document. Organizations should prioritize the deployment of this update, particularly in environments where users regularly process documents from external sources or receive email attachments.

Attack Vectors

The primary attack vectors for these vulnerabilities include:

• Malicious Word documents distributed via email or web downloads
• Compromised websites hosting exploit documents
• Email attachments containing embedded exploits
• Network shares containing malicious Office files

Mitigation Strategies

While installing KB5002839 is the primary mitigation, organizations can implement additional protective measures:

• Enable Office Protected View for documents from untrusted sources
• Configure macro security settings to disable macros by default
• Implement email security solutions to scan attachments
• Educate users about the risks of opening untrusted documents

Post-Installation Verification

After installing KB5002839, administrators should verify successful deployment through several methods:

Version Verification

Check the Office application version by opening Word 2016 or Outlook 2016 and navigating to File > Account > About [Application]. The version information should reflect the February 2026 update.

Registry Verification

For MSI-based installations, verify the update installation through the Windows Registry. The update should be listed under:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\

Event Log Monitoring

Monitor Windows Event Logs for any installation errors or warnings related to the Office update process. Successful installations should generate corresponding entries in the Application event log.

Enterprise Deployment Considerations

Large organizations should consider the following factors when deploying KB5002839:

Testing and Validation

Before widespread deployment, test the update in a controlled environment to identify potential compatibility issues with existing workflows, custom applications, or third-party add-ins.

Phased Rollout

Implement a phased rollout strategy, beginning with pilot groups and gradually expanding to the entire organization. This approach allows for early identification and resolution of deployment issues.

User Communication

Communicate the update deployment to end users, including any expected changes in application behavior or new security prompts they may encounter.

Compliance and Regulatory Considerations

Organizations subject to regulatory compliance requirements should document the installation of KB5002839 as part of their security patch management processes. The update addresses vulnerabilities that could impact data confidentiality and system integrity, making it relevant for various compliance frameworks including SOX, HIPAA, and PCI DSS.