CVE-2026-64909: Microsoft 365 Apps

High severity, CVSS 7.8. EPSS: 0.5% chance of exploitation in the next 30 days.

Integer underflow (wrap or wraparound) in Microsoft Office allows an unauthorized attacker to execute code locally.

Affected products

• Microsoft 365 Apps: affected versions not specified
• Microsoft Microsoft 365: affected versions not specified
• Microsoft Office 2016: affected versions not specified
• Microsoft Office 2019: affected versions not specified
• Microsoft Office 2021: affected versions not specified
• Microsoft Office 2024: affected versions not specified

Published 2026-08-11. Last modified 2026-08-14.