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Microsoft Teams Guest Access Vulnerability Exposes Users to Security Risks

Microsoft Teams Guest Access Vulnerability Exposes Users to Security Risks

First seen 28 Nov 2025, 09:36 UTC • •

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ThreatCluster AI
ThreatCluster •March 12, 2026 at 13:27 UTC

A report from Ontinue reveals that Microsoft Teams' guest access feature allows users to accept invitations from external organizations, which results in the loss of their Defender for Office 365 protections. This vulnerability enables potential attacks as users interact with unprotected environments while logged in with their corporate accounts. Ontinue's threat researcher, Rhys Downing, highlights that this issue is linked to a feature enabling chats with any email address.

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