Microsoft Blocks MSIX Attachments in Outlook
ID: 89251b57-4c6a-5f7e-9135-4e5ab76303b0
STIX ID: report--89251b57-4c6a-5f7e-9135-4e5ab76303b0
Feed Name: securityonline.info
Threat Score
Microsoft will add MSIX and MSIXBundle to the blocked file types in Exchange Online (affecting Outlook on the web and the new Outlook client) starting November 2026, after Threat Intelligence observed financially motivated groups abusing the App Installer protocol to distribute malicious MSIX packages masquerading as legitimate software; enterprises can configure exceptions for internal workflows but downloads and openings will be restricted by default.
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