Summary
| Vulnerability Name | Security Feature Bypass in Microsoft Office (CVE-2026-21509) |
| Released on | January 27, 2026 |
| Affected Component | Microsoft Office |
| Affected Version |
Microsoft Office 2016
Microsoft Office 2019
Microsoft Office LTSC 2021
Microsoft Office LTSC 2024
Microsoft 365 Apps for Enterprise
|
| Vulnerability Type | Authentication bypass |
| Exploitation Condition |
1. User authentication: not required.
2. Precondition: default configurations.
3. Trigger mode: local.
|
| Impact | Exploitation difficulty: easy. Unauthorized attackers can exploit this vulnerability to bypass authentication. Severity: critical. This vulnerability can result in authentication bypass. |
| Official Solution | Available |
About the Vulnerability
Component Introduction
Microsoft Office is a world-leading office suite developed by Microsoft. Its core components include Word for word processing, Excel for spreadsheets, PowerPoint for presentations, Outlook for email management, and Access for database applications. Microsoft Office can run on Windows, macOS, and mobile platforms. Through Microsoft 365 cloud services, it enables real-time collaboration and provides a variety of advanced features. Due to its powerful compatibility, rich toolsets, and extensive enterprise integration capabilities, Microsoft Office has become a foundational productivity platform for individuals and enterprises to perform file processing, data analysis, and team collaboration.
Vulnerability Description
On January 27, 2026, Sangfor FarSight Labs received notification of the security feature bypass vulnerability in Microsoft Office (CVE-2026-21509), classified as critical in threat level.
Specifically, Microsoft Office contains a security feature bypass vulnerability. Attackers can exploit this vulnerability to craft malicious documents to bypass the protection mechanism that Microsoft Office provides to protect users from vulnerable object linking and embedding (OLE) controls. Successful exploitation requires an attacker to send a specially crafted Office file and persuade a user to open it. This vulnerability has been detected in active exploitation in the wild.
Affected Versions
The following Microsoft Office versions are affected:
Microsoft Office 2016
Microsoft Office 2019
Microsoft Office LTSC 2021
Microsoft Office LTSC 2024
Microsoft 365 Apps for Enterprise
Solutions
Remediation Solutions
Official Solutions
The latest versions have been officially released to fix the vulnerability. Affected users are advised to update Microsoft Office to the corresponding latest version:
Temporary Solutions
- Disable unused functional modules to reduce attack entry points.
- Follow the principle of least privilege to strictly control the scope of permissions for sensitive operations.
- Do not expose services to the Internet unless necessary, to limit the access sources to trusted ranges.
- Regularly update the system and components to secure versions so that known vulnerabilities can be patched at the earliest opportunity.
Sangfor Solutions
Risky Asset Discovery
The following Sangfor service can proactively detect CVE-2026-21509 vulnerabilities and quickly discover affected assets in batches in business scenarios:
- Athena Endpoint Protection Platform (EPP): The corresponding asset discovery solution has been released. The fingerprint ID is 0001936.
Timeline
On January 27, 2026, Sangfor FarSight Labs received notification of the security feature bypass vulnerability in Microsoft Office (CVE-2026-21509).
On January 27, 2026, Sangfor FarSight Labs released a vulnerability alert.
Reference
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509
Learn More
Sangfor FarSight Labs researches the latest cyber threats and unknown zero-day vulnerabilities, alerting customers to potential dangers to their organizations, and providing real-time solutions with actionable intelligence. Sangfor FarSight Labs works with other security vendors and the security community at large to identify and verify global cyber threats, providing fast and easy protection for customers.
