CVE-2021-43256: Microsoft Excel Remote Code Execution Vulnerability

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 2.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-12-15 · updated 2026-06-17

Description

Microsoft Excel Remote Code Execution Vulnerability

Affected products

Microsoft 365 Apps: all versions
Microsoft Excel 2013 Service Pack 1: 2013-sp1, 2016
Microsoft Excel Rt: 2013-sp1
Microsoft Office: 2019
Microsoft Office LTSC for Mac 2021: 2021
Microsoft Office Online Server: all versions
Microsoft Office Web Apps: 2013-sp1
Microsoft 365 Apps: from 16.0.1 before https://aka.ms/OfficeSecurityReleases — fixed in https://aka.ms/OfficeSecurityReleases
Microsoft Excel 2013 Service Pack 1: from 15.0.0.0 before 15.0.5407.1000 — fixed in 15.0.5407.1000
Microsoft Excel 2016: from 16.0.0.0 before 16.0.5254.1000 — fixed in 16.0.5254.1000
Microsoft Office LTSC 2021: from 16.0.1 before https://aka.ms/OfficeSecurityReleases — fixed in https://aka.ms/OfficeSecurityReleases
Microsoft Office Web Apps Server 2013 Service Pack 1: from 15.0.1 before 15.0.5407.1000 — fixed in 15.0.5407.1000
Microsoft Office: from 19.0.0 before https://aka.ms/OfficeSecurityReleases — fixed in https://aka.ms/OfficeSecurityReleases
Microsoft Office Online Server: from https://aka.ms/OfficeSecurityReleases before 16.0.10381.20001 — fixed in 16.0.10381.20001

How to fix

Upgrade to a fixed version: Microsoft 365 Apps https://aka.ms/OfficeSecurityReleases; Microsoft Excel 2013 Service Pack 1 15.0.5407.1000; Microsoft Excel 2016 16.0.5254.1000; Microsoft Office LTSC 2021 https://aka.ms/OfficeSecurityReleases; Microsoft Office Web Apps Server 2013 Service Pack 1 15.0.5407.1000; Microsoft Office https://aka.ms/OfficeSecurityReleases; Microsoft Office Online Server 16.0.10381.20001. Check the vendor advisory for mitigations.

References

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