Microsoft Office 0-day vulnerability CVE-2026-21509; Emergency updates available

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Microsoft Office 0-day vulnerability CVE-2026-21509; Emergency updates available

Borncity • January 27, 2026

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Microsoft Office 2016 to 2024 and Office 365 apps contain a zero - day vulnerability (CVE-2026-21509) that is being actively exploited in attacks.

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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 Office 0-day Vulnerability CVE-2026-21509 Exploited; Emergency Fix Released Microsoft Office 2016 to 2024 and Office 365 apps are affected by a zero-day vulnerability (CVE-2026-21509) that is currently being exploited in attacks. Microsoft has released emergency security updates to address this issue. 7 sources 94

Extracted Entities

Attack Types (1)

Zero-day Exploit

CVEs (1)

Platforms (1)

Microsoft Office