Emergency Microsoft update fixes in-the-wild Office zero-day
ID: 4a707d9e-c8e3-5f7e-8739-4a26b36be2e1
STIX ID: report--4a707d9e-c8e3-5f7e-8739-4a26b36be2e1
Feed Name: Security Affairs
Threat Score
Microsoft released emergency out-of-band updates for CVE-2026-21509, an actively exploited Office zero-day that bypasses OLE/COM security protections in Office 2016–2024 and Microsoft 365 Apps; Microsoft confirmed active exploitation, provided mitigations (service-side fixes for Office 2021+ and registry-based workarounds or pending updates for 2016/2019), and withheld technical details of observed attacks.
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