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Microsoft · Office

CVE-2026-21509

Microsoft Office Security Feature Bypass Vulnerability

CISA KEV record

CISA date added
2026-01-26
CISA due date
2026-02-16
Known ransomware use
Unknown

NVD risk context

7.8 HIGH

CVSS is a technical severity score. CISA’s KEV status remains the evidence that this vulnerability is known to be exploited.

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Attack vector
Local
An attacker needs local access to the affected system.
Attack complexity
Low
Exploitation does not require unusual conditions beyond normal attacker control.
Privileges required
None
The attacker does not need an existing account or privileges.
User interaction
Required
A user must take an action, such as opening a file or link.

Description

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.

NVD reference index

Vendor and remediation references

NVD has tagged these sources as vendor advisories, patches, mitigations, or release notes.

Other NVD references (2)

MITRE CWE context

CWE classification

CWE-807 Reliance on Untrusted Inputs in a Security Decision

The product uses a protection mechanism that relies on the existence or values of an input, but the input can be modified by an untrusted actor in a way that bypasses the protection mechanism.

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NVD record timing

NVD record timeline

These dates describe NVD’s record, not CISA’s KEV addition or remediation due date.

NVD published
Jan 26, 2026, 06:16 PM UTC
When NVD first published this CVE record.
NVD last updated
Jun 25, 2026, 05:16 AM UTC
When NVD last changed its analysis or record data.
Advanced: view the technical CVSS vector

This standardized code is intended for security tools and technical analysts. The plain-language risk summary above explains its main points.

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

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CISA notes

Please adhere to Microsoft’s recommended guidelines to address this vulnerability. Implement all final mitigations provided by the vendor for Office 2021, and apply the interim corresponding mitigations for Office 2016 and Office 2019 until the final patch becomes available. For more information please see: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509 ; https://nvd.nist.gov/vuln/detail/CVE-2026-21509