Microsoft Teams Flaw in Guest Chat Exposes Users to Malware Attacks

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November 26, 2025 at 4:13 PM

Summary

New research highlights a significant security vulnerability in Microsoft Teams B2B Guest Access, allowing attackers to circumvent Defender for Office 365 protections with just a single invitation. This flaw poses a serious risk of malware attacks on users, emphasizing the need for immediate attention to security protocols within the platform.

Original Article Summary

New research from Ontinue exposes a major security flaw in Microsoft Teams B2B Guest Access. Learn how attackers bypass all Defender for Office 365 protections with a single invite.

Impact

Microsoft Teams B2B Guest Access, Defender for Office 365

In the Wild

Unknown

Timeline

Newly disclosed

Remediation

Users should review and tighten guest access permissions in Microsoft Teams, implement additional security measures, and monitor for suspicious activities. Regular updates and patches for Defender for Office 365 should also be applied as they become available.

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