CVE-2026-55949: Microsoft Excel Remote Code Execution Vulnerability

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-14 · updated 2026-10-28
Weakness: CWE-908

Description

Use of uninitialized resource in Microsoft Office Excel allows an unauthorized attacker to execute code locally.

Affected products

Microsoft 365 Apps: all versions
Microsoft Excel 2013 Service Pack 1: 2016
Microsoft 365: all versions
Microsoft Office 2019: all versions
Microsoft Office 2021: all versions
Microsoft Office LTSC 2024: all versions
Microsoft Office Online Server: before 16.0.10417.20175 — fixed in 16.0.10417.20175
Microsoft 365 Apps: from 16.0.1 before https://aka.ms/OfficeSecurityReleases — fixed in https://aka.ms/OfficeSecurityReleases
Microsoft Excel 2016: from 16.0.0.0 before 16.0.5561.1001 — fixed in 16.0.5561.1001
Microsoft Office 365 for Mac: from 1.0.0 before 16.111.26071215 — fixed in 16.111.26071215
Microsoft Office LTSC 2021: from 16.0.1 before https://aka.ms/OfficeSecurityReleases — fixed in https://aka.ms/OfficeSecurityReleases
Microsoft Office LTSC for Mac 2024: from 16.0.0 before 16.111.26071215 — fixed in 16.111.26071215
Microsoft Office: from 19.0.0 before https://aka.ms/OfficeSecurityReleases — fixed in https://aka.ms/OfficeSecurityReleases
Microsoft Office LTSC 2024: from 16.0.0 before https://aka.ms/OfficeSecurityReleases — fixed in https://aka.ms/OfficeSecurityReleases
Microsoft Office LTSC for Mac 2021: from 16.0.1 before 16.111.26071215 — fixed in 16.111.26071215
Microsoft Office Online Server: from 16.0.0.0 before 16.0.10417.20175 — fixed in 16.0.10417.20175

How to fix

Upgrade to a fixed version: Microsoft Office Online Server 16.0.10417.20175; Microsoft 365 Apps https://aka.ms/OfficeSecurityReleases; Microsoft Excel 2016 16.0.5561.1001; Microsoft Office 365 for Mac 16.111.26071215; Microsoft Office LTSC 2021 https://aka.ms/OfficeSecurityReleases; Microsoft Office LTSC for Mac 2024 16.111.26071215; Microsoft Office https://aka.ms/OfficeSecurityReleases; Microsoft Office LTSC 2024 https://aka.ms/OfficeSecurityReleases; Microsoft Office LTSC for Mac 2021 16.111.26071215; Microsoft Office Online Server 16.0.10417.20175. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55949

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