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Vulnerabilities

Vulnerability · CVE-2026-21509

Microsoft Office Security Feature Bypass Vulnerability

Published Jan 26, 2026 · catalog updated Jun 24, 2026 · Microsoft Office

Patch now

CVE-2026-21509 is in the CISA known-exploited catalog, due Feb 16, 2026. Confirm Microsoft Office against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
Severity
High7.8
Known exploitation
CISA KEV and VulnCheck KEV
EPSS
70.80%
Remediation
Remediation guidance
Affected products
cpe microsoft/365 apps · cpe microsoft/office · cpe microsoft/office long term servicing channel · vendor Microsoft Office

Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe microsoft/365 appsversion unspecified
  • cpe microsoft/office2016
  • cpe microsoft/office2019
  • cpe microsoft/office long term servicing channel2021
  • vendor Microsoft Officeversion unspecified

How to fix CVE-2026-21509

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

CVE-2026-21509 is in the CISA known-exploited catalog, due Feb 16, 2026. Confirm Microsoft Office against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Which versions are affected?

Compare what you have installed with microsoft/office long term servicing channel 2021. Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

What should an analyst verify?

CWE-807. EPSS 70.80%. The CISA KEV listing is the exploitation evidence. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Jan 26, 2026 · Catalog

    Detected

    Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.

  2. Jan 26, 2026 · CISA KEV

    Known exploited

    Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

  3. Feb 16, 2026 · CISA KEV

    Remediation due

    Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

  4. Jun 24, 2026 · Catalog

    Updated

    Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.

Sources

  • CISA KEVConfirmed exploitationCVE-2026-21509

    Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.

    cisa.gov
  • CVE.orgVulnerability recordCVE-2026-21509

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-21509

    30-day exploitation probability 70.8%

    first.org
  • NIST NVDVulnerability recordCVE-2026-21509

    Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

    nvd.nist.gov
  • VulnCheck KEVConfirmed exploitationCVE-2026-21509

    Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL)

    vulncheck.com

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.