CVE-2026-77902: Microsoft Office Excel Remote Code Execution Vulnerability

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-13 · updated 2026-10-29
Weakness: CWE-122

Description

Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.

Affected products

Microsoft 365 Apps: all versions
Microsoft 365: all versions
Microsoft Office 2021: all versions
Microsoft Office LTSC 2024: all versions
Microsoft 365 Apps: from 16.0.1 before https://aka.ms/OfficeSecurityReleases — fixed in https://aka.ms/OfficeSecurityReleases
Microsoft Office 365 for Mac: from 1.0.0 before 16.114.26101123 — fixed in 16.114.26101123
Microsoft Office LTSC 2021: from 16.0.1 before 16.0.14334.20974 — fixed in 16.0.14334.20974
Microsoft Office LTSC for Mac 2024: from 16.0.0 before 16.114.26101123 — fixed in 16.114.26101123
Microsoft Office LTSC 2024: from 16.0.0 before 16.0.17932.21056 — fixed in 16.0.17932.21056
Microsoft Office LTSC for Mac 2021: from 16.0.1 before 16.114.26101123 — fixed in 16.114.26101123

How to fix

Upgrade to a fixed version: Microsoft 365 Apps https://aka.ms/OfficeSecurityReleases; Microsoft Office 365 for Mac 16.114.26101123; Microsoft Office LTSC 2021 16.0.14334.20974; Microsoft Office LTSC for Mac 2024 16.114.26101123; Microsoft Office LTSC 2024 16.0.17932.21056; Microsoft Office LTSC for Mac 2021 16.114.26101123. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-77902

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