CVE-2026-42831: Microsoft 365 Copilot

High severity, CVSS 7.8. EPSS: 0.5% 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 Copilot: before 16.0.19822.20190 (fixed in 16.0.19822.20190)
• Microsoft Office: version 2024 only
• Microsoft Office Long Term Servicing Channel: version 2021 only

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