CVE-2026-42831: Microsoft Office Remote Code Execution Vulnerability

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-12 · updated 2026-10-26
Weakness: CWE-122

Description

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: 2024
Microsoft Office LTSC for Mac 2021: 2021
Microsoft Office for Android: from 16.0.1 before 16.0.19822.20190 — fixed in 16.0.19822.20190
Microsoft Office LTSC for Mac 2024: from 16.0.0 before 16.109.26051019 — fixed in 16.109.26051019
Microsoft Office LTSC for Mac 2021: from 16.0.1 before 16.109.26051019 — fixed in 16.109.26051019

How to fix

Upgrade to a fixed version: Microsoft 365 Copilot 16.0.19822.20190; Microsoft Office for Android 16.0.19822.20190; Microsoft Office LTSC for Mac 2024 16.109.26051019; Microsoft Office LTSC for Mac 2021 16.109.26051019. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42831

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