CVE-2026-40363: Microsoft 365 Apps

High severity, CVSS 8.4. EPSS: 0.4% chance of exploitation in the next 30 days.

Heap-based buffer overflow in Microsoft Office allows an unauthorized attacker to execute code locally.

Affected products

• Microsoft 365 Apps: affected versions not specified
• Microsoft 365 Copilot: before 16.0.19822.20190 (fixed in 16.0.19822.20190)
• Microsoft Office: version 2016 only; version 2019 only
• Microsoft Office Long Term Servicing Channel: version 2021 only; version 2024 only

Published 2026-05-12. Last modified 2026-06-17.