MC1125497 - External workbook links to blocked file types will be disabled by default

Introduction

To enhance workbook security, a new group policy is being introduced to expand File Block Settings to external workbook links. This policy allows administrators to control whether links to blocked file types can be refreshed.

If not configured, no changes will take effect immediately. However, starting October 2025, the default behavior will block external links to file types currently blocked by the Trust Center. When this policy is enabled, new references to blocked file types will return a #BLOCKED error. Existing links will display the last successfully refreshed values but will no longer refresh.

When this will happen

General Availability: We will begin rolling out the default change in early October 2025 and end in late July 2026.

How this affects your organization

• Policy not configured: No immediate change will occur.
• Build 2509 warning bar: Users will see a business bar when opening workbooks containing external links to blocked file types, alerting them to the upcoming change.
• Build 2510 enforcement: If the policy remains unconfigured, users will no longer be able to refresh or create new references to blocked file types.
• Existing links behavior: External links will retain the last successfully loaded value but will not refresh.
• New links behavior: Creating a new external link to a blocked file type will return a #BLOCKED error.
• Workbook Links pane: Will indicate which workbooks failed to refresh due to being blocked.

What you can do to prepare

Administrators who need to allow workbook links to blocked file types can revert to the previous behavior using the following methods:

• Registry setting: Set HKCU\Software\Microsoft\Office\16.0\Excel\Security\FileBlock\FileBlockExternalLinks to 0.
• Group Policy setting: Set File Block Includes External Link Files to Disabled:
• Excel Group Policy Template > Excel Options > Security > Trust Center > File Block Settings > File Block includes external link files

We recommend reviewing existing workbooks and communicating this change to users who rely on external links to ensure continuity of workflows.

Learn more: Macros from the internet are blocked by default in Office

Learn more: External Workbook Links to Blocked File Types Will Be Disabled by Default

Compliance considerations

No compliance considerations identified, review as appropriate for your organization.