Microsoft Office Security Feature Bypass Vulnerability

CVE	CVE-2026-21509
State	PUBLISHED
Assigner	microsoft
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-01-26 18:16:38 UTC
Updated	2026-06-25 05:16:53 UTC
Description	Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

Primary CVSS: v3.1 7.8 HIGH from [email protected]

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

EPSS: 0.721520000 probability, percentile 0.993570000 (date 2026-07-02)

CISA KEV: Listed on 2026-01-26; due 2026-02-16; ransomware use Unknown

Problem Types: CWE-807 | CWE-807 CWE-807: Reliance on Untrusted Inputs in a Security Decision

Version	Source	Type	Score	Severity	Vector
3.1	[email protected]	Secondary	7.8	HIGH	`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`
3.1	CNA	CVSS	7.8	HIGH	`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C`

Attack Vector

Local

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

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

Vendor	Microsoft
Product	Office
Name	Microsoft Office Security Feature Bypass Vulnerability
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.
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

Type	Vendor	Product	Version	Update	Edition	Language
Application	Microsoft	365 Apps	-	All	All	All
Application	Microsoft	365 Apps	-	All	All	All
Application	Microsoft	Office	2016	All	All	All
Application	Microsoft	Office	2016	All	All	All
Application	Microsoft	Office	2019	All	All	All
Application	Microsoft	Office	2019	All	All	All
Application	Microsoft	Office Long Term Servicing Channel	2021	All	All	All
Application	Microsoft	Office Long Term Servicing Channel	2021	All	All	All
Application	Microsoft	Office Long Term Servicing Channel	2024	All	All	All
Application	Microsoft	Office Long Term Servicing Channel	2024	All	All	All

Source	Vendor	Product	Version	Platforms
CNA	Microsoft	Microsoft 365 Apps For Enterprise	affected 16.0.1 https://aka.ms/OfficeSecurityReleases custom	32-bit Systems, x64-based Systems
CNA	Microsoft	Microsoft Office 2016	affected 16.0.0 16.0.5539.1001 custom	32-bit Systems, x64-based Systems
CNA	Microsoft	Microsoft Office 2019	affected 19.0.0 16.0.10417.20095 custom	32-bit Systems, x64-based Systems
CNA	Microsoft	Microsoft Office LTSC 2021	affected 16.0.1 https://aka.ms/OfficeSecurityReleases custom	32-bit Systems, x64-based Systems
CNA	Microsoft	Microsoft Office LTSC 2024	affected 16.0.0 https://aka.ms/OfficeSecurityReleases custom	32-bit Systems, x64-based Systems

Reference	Source	Link	Tags
www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-offi...	af854a3a-2127-422b-91ae-364da2661108	www.vicarius.io	Third Party Advisory
msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509	[email protected]	msrc.microsoft.com	Vendor Advisory
www.cisa.gov/known-exploited-vulnerabilities-catalog	134c704f-9b21-4f2e-91b3-4a467353bcc0	www.cisa.gov	US Government Resource
www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-off...	af854a3a-2127-422b-91ae-364da2661108	www.vicarius.io	Mitigation, Third Party Advisory
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis
CISA Known Exploited Vulnerabilities catalog	CISA	www.cisa.gov	kev

No vendor comments have been submitted for this CVE.

There are currently no legacy QID mappings associated with this CVE.