Microsoft releases update to address zero-day vulnerability in Microsoft Office
Summary: CVE-2026-21509 is a security feature bypass vulnerability in Microsoft Office rated Important with a CVSS 3.1 score of 7.8, triggered locally by an attacker with system access or by a victim opening a malicious Office document. It has been added to CISA's Known Exploited Vulnerabilities list, Microsoft reports it cannot be triggered through the Preview Pane, and Talos released Snort2 rules 65823-65830 and Snort3 rules 301384-301387 to detect exploitation attempts.
Key Takeaway: The flaw is already on CISA's Known Exploited Vulnerabilities list, meaning exploitation has been observed in the wild, and it arrives alongside Microsoft's November 2026 update covering 1,328 vulnerabilities, 60 of them critical and 45 of those remote code execution.
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- Topics
- Vulnerabilities & Patching
- Mentions
- CVE-2026-21509
- Related
- CVE-2026-21509: Microsoft Office Security Feature Bypass Vulnerability Known Exploited Vulnerabilities · Jan 26, 2026