CVE-2026-21509
highpriority · act · 90OT risk · criticalKEV · exploitedEPSS 0.708 · 99 %ileexploit · PoCDEEUNLRUUSadded 2026-01-26remediate by 2026-02-16
required action Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
EPSS · scored 2026-10-26
Microsoft Office Security Feature Bypass Vulnerability
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
remediations
Vendor fix, mitigation, or workaround guidance, as published by each source.
A vendor fix is available.
- FixedMicrosoft 365 Apps for Enterprise for 32-bit Systemsmsrc_csaf
https://aka.ms/OfficeSecurityReleases:Security Update:https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates
https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates - FixedMicrosoft 365 Apps for Enterprise for 64-bit Systemsmsrc_csaf
https://aka.ms/OfficeSecurityReleases:Security Update:https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates
https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates - FixedMicrosoft Office 2016 (32-bit edition)msrc_csaf
16.0.5539.1001:Security Update:https://support.microsoft.com/help/5002713
https://support.microsoft.com/help/5002713 - FixedMicrosoft Office 2016 (64-bit edition)msrc_csaf
16.0.5539.1001:Security Update:https://support.microsoft.com/help/5002713
https://support.microsoft.com/help/5002713 - FixedMicrosoft Office 2019 for 32-bit editionsmsrc_csaf
16.0.10417.20095:Security Update:https://learn.microsoft.com/en-us/officeupdates/update-history-office-2019
https://learn.microsoft.com/en-us/officeupdates/update-history-office-2019 - FixedMicrosoft Office 2019 for 64-bit editionsmsrc_csaf
16.0.10417.20095:Security Update:https://learn.microsoft.com/en-us/officeupdates/update-history-office-2019
https://learn.microsoft.com/en-us/officeupdates/update-history-office-2019 - FixedMicrosoft Office LTSC 2021 for 32-bit editionsmsrc_csaf
https://aka.ms/OfficeSecurityReleases:Security Update:https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates
https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates - FixedMicrosoft Office LTSC 2021 for 64-bit editionsmsrc_csaf
https://aka.ms/OfficeSecurityReleases:Security Update:https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates
https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates - FixedMicrosoft Office LTSC 2024 for 32-bit editionsmsrc_csaf
https://aka.ms/OfficeSecurityReleases:Security Update:https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates
https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates - FixedMicrosoft Office LTSC 2024 for 64-bit editionsmsrc_csaf
https://aka.ms/OfficeSecurityReleases:Security Update:https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates
https://docs.microsoft.com/en-us/officeupdates/office365-proplus-security-updates
cvss
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode
ssvc
A stakeholder decision — act, attend, or track — from exploitation and impact.
weaknesses
The CWE weakness classes this flaw belongs to.
exploits (13)
Public proof-of-concept and weaponised exploit code.
- DameDode/CVE-2026-21509-POCPOC for the Office vulnerabilityPoC · poc_in_github
affected products (56)
Products and version ranges known to be affected.
- Microsoft Microsoft Office LTSC 2021all versionscert_bundDEcpe:/a:microsoft:microsoft_office_ltsc_2021:-
- Microsoft Microsoft Office LTSC 2024all versionscert_bundDEcpe:/a:microsoft:microsoft_office_ltsc_2024:-
- Microsoft Microsoft 365 Apps for Enterprise16.0.1 → https://aka.ms/OfficeSecurityReleasesenisa_euvdEU
- Microsoft Microsoft 365 Apps for Enterprise for 32-bit Systems< https://aka.ms/OfficeSecurityReleasesmsrc_csafUS
- Microsoft Microsoft 365 Apps for Enterprise for 64-bit Systems< https://aka.ms/OfficeSecurityReleasesmsrc_csafUS
advisories (3)
Vendor and ecosystem advisories describing this.
- NCSC-2026-0039ZeroDay kwetsbaarheid verholpen in Microsoft OfficeNL2026-01-27csaf · ncsc_nlNL
Microsoft heeft een ZeroDay kwetsbaarheid verholpen in Microsoft Office.
- WID-SEC-W-2026-0221Microsoft Office-Produkte und Microsoft 365-Apps: Schwachstelle ermöglicht Umgehen von SicherheitsvorkehrungenDeutsch2026-01-26csaf · cert_bundDE
Ein lokaler Angreifer kann eine Schwachstelle in Microsoft Office 2016, Office 2019, Office LTSC 2021, Office LTSC 2024 und Microsoft 365 Apps for Enterprise ausnutzen, um Sicherheitsvorkehrungen zu umgehen.
- msrc_CVE-2026-21509Microsoft Office Security Feature Bypass Vulnerability2026-01-26csaf · msrc_csafUS
To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle
also known as (4)
Other names and identifiers for this entity.
sources
Which sources assert this record, and when.
references (9)
External citations — patches, advisories, analysis.
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509cnnvd
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509cnnvd
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerabilitycnnvd
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerabilitycnnvd
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509enisa_euvd
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509Vendor Advisorynvd
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509US Government Resourcenvd
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerabilityThird Party Advisorynvd
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