Microsoft Teams Guest Chat Vulnerability Exposes Users to Malware Attacks

Cyberpress • November 27, 2025

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A newly uncovered vulnerability in Microsoft Teams puts millions of corporate users at risk of sophisticated malware attacks that can bypass even ...

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This article is one source in a clustered incident — the cluster page carries the summary, timeline and every other outlet covering it.

Microsoft Teams Guest Access Vulnerability Exposes Users to Security Risks 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. 22 sources 26

Extracted Entities

Attack Types (1)

Tools (1)

Microsoft Teams

Vulnerabilities (1)

Microsoft Teams Guest Chat Vulnerability