Microsoft Teams and Defender for Office 365 add centralized external-user blocking controls
Security Tool/Service
Summary
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Microsoft Teams is gaining centralized controls that let security admins block external users, suspicious domains, and malicious content handling in Defender for Office 365, reducing the risk of social-engineering abuse across organizational messaging and meetings. The update matters because it moves external communication restrictions into the Defender portal and strengthens default messaging protections for January 2026 rollout.
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Sources 1
About this happening:
Microsoft rolled out security updates for Defender and related malware protection components to address two zero-days: CVE-2026-41091 and CVE-2026-45498. The fixes cover affected...
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Timeline
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24.12.2025 18:22 2 articles · 5mo ago
Microsoft announces Teams external-user blocking controls
Initial DisclosureMicrosoft announced that Teams security administrators will soon be able to block external users from sending messages, calls, or meeting invitations to people in their organization through the Microsoft Defender portal. The update integrates Teams with Defender for Office 365, lets admins manage blocked external contacts through the Tenant Allow/Block List, and will begin rolling out in early January 2026 with completion expected by mid-January 2026. Before use, organizations must enable two disabled-by-default Teams admin center settings, and the feature will work across the Defender XDR web portal and all Teams clients without changing existing domain blocks or federation configurations.
Show sources
- Microsoft Teams to let admins block external users via Defender portal — www.bleepingcomputer.com — 24.12.2025 18:22
- Microsoft Teams to let admins block external users via Defender portal — www.bleepingcomputer.com — 24.12.2025 18:22