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Findings

CVE-2026-21509

Microsoft Office Security Feature Bypass Vulnerability

Published Jan 26, 2026 · updated Jun 24, 2026 · 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.

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.

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.

CISA due date Feb 16, 2026

Affected

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

Sources

  • CISA KEVCVE-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.orgCVE-2026-21509

    Official CVE identifier

    cve.org
  • FIRST EPSSCVE-2026-21509

    30-day exploitation probability 70.8%

    first.org
  • NIST NVDCVE-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

References