Microsoft Teams to allow custom blocking of file extensions for security

Customizable File Extension Blocking

Microsoft Teams will update its Weaponizable File Protection feature to allow administrators to customize the list of blocked file extensions. This change addresses the current limitation where admins cannot modify the default list of file types considered dangerous. The update aims to help organizations align Teams' security settings with their specific security requirements.

The new functionality will apply to file attachments in chat and channel messages, scanning them for high-risk extensions and blocking those identified. This provides greater flexibility for tailoring file protection policies while maintaining a secure collaboration environment within Teams.

Rollout Timeline and Availability

According to the Microsoft 365 roadmap, this feature is currently under development and is slated to begin rolling out in November 2026. Once generally available, it will be accessible across Android, desktop, iOS, macOS, and web platforms. The update will be available for standard multi-tenant cloud environments globally.

Broader Security Enhancements in Teams

This file extension customization is part of a series of security improvements for Microsoft Teams. Starting in December, administrators will gain the ability to block external users via the Defender portal to counter social engineering attacks. Earlier this month, Microsoft announced a new security feature to blur QR codes from external senders to protect against phishing and fraud.

Additionally, Microsoft will enable users to report suspicious guest invitations directly from Teams starting in November, assisting security teams in identifying and blocking phishing attempts. A new Teams meeting protection policy is also rolling out, allowing admins to automatically block identified external bots from joining meetings.