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CVE-2026-21509— Microsoft Office Security Feature Bypass Vulnerability

Quick assessment

Affected
Microsoft Microsoft 365 Apps for Enterprise
Exploitation
Confirmed exploitation in the wild; remediate immediately
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Microsoft Office是美国微软（Microsoft）公司的一款办公软件套件产品。该产品常用组件包括Word、Excel、Access、Powerpoint、FrontPage等。 Microsoft Office存在安全漏洞，该漏洞源于安全决策依赖不可信输入，可能导致本地攻击者绕过安全功能。

CVSS 7.8 · High KEV EPSS 70.80% · P99

Possible ATT&CK Techniques 1 AI

T1078 · Valid Accounts

Affected Version Matrix 5

VendorProduct Version RangeStatus
Microsoft Microsoft 365 Apps for Enterprise 16.0.1< https://aka.ms/OfficeSecurityReleases affected
Microsoft Microsoft Office 2016 16.0.0< 16.0.5539.1001 affected
Microsoft Microsoft Office 2019 19.0.0< 16.0.10417.20095 affected
Microsoft Microsoft Office LTSC 2021 16.0.1< https://aka.ms/OfficeSecurityReleases affected
Microsoft Microsoft Office LTSC 2024 16.0.0< https://aka.ms/OfficeSecurityReleases affected
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I. Basic Information for CVE-2026-21509

Vulnerability Information
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Vulnerability Title
Microsoft Office Security Feature Bypass Vulnerability
Source: CVE Program / CVE List V5
Vulnerability Description
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
在安全决策中依赖未经信任的输入
Source: CVE Program / CVE List V5
Vulnerability Title
Microsoft Office 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Microsoft Office是美国微软（Microsoft）公司的一款办公软件套件产品。该产品常用组件包括Word、Excel、Access、Powerpoint、FrontPage等。 Microsoft Office存在安全漏洞，该漏洞源于安全决策依赖不可信输入，可能导致本地攻击者绕过安全功能。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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Affected Products

Vendor Product Affected Versions CPE Subscribe
Microsoft Microsoft 365 Apps for Enterprise 16.0.1 ~ https://aka.ms/OfficeSecurityReleases -
Microsoft Microsoft Office 2016 16.0.0 ~ 16.0.5539.1001 -
Microsoft Microsoft Office 2019 19.0.0 ~ 16.0.10417.20095 -
Microsoft Microsoft Office LTSC 2021 16.0.1 ~ https://aka.ms/OfficeSecurityReleases -
Microsoft Microsoft Office LTSC 2024 16.0.0 ~ https://aka.ms/OfficeSecurityReleases -

II. Public POCs for CVE-2026-21509

# POC Description Source Link Shenlong Link
1 CVE-2026-21509 https://github.com/kimstars/Ashwesker-CVE-2026-21509 POC Details
2 Educational PoC for CVE‑2026‑21509 (Microsoft Office security feature bypass). Generates a harmless DOCX with dummy OLE artifacts to study EDR/AV visibility. Not an exploit. For isolated labs only; see README for 7‑Zip inspection steps and mitigation references. https://github.com/gavz/CVE-2026-21509-PoC POC Details
3 Powershell script with Detection and Remediation for CVE-2026-21509 https://github.com/ksk-itdk/KSK-ITDK-CVE-2026-21509-Mitigation POC Details
4 New Physics Disclosure This repository contains a full weaponized exploit for **CVE-2026-21509**, targeting the Windows Network File System (NFSv4.1) kernel-mode driver (`nfssvr.sys`). https://github.com/SimoesCTT/CTT-NFS-Vortex-RCE POC Details
5 Microsoft just released emergency patches for CVE-2026-21509, a zero-day in the Office Suite that bypasses OLE/COM mitigations when a user simply opens a file. They think their "Service-side change" for Office 2021+ is a solid wall. https://github.com/SimoesCTT/SCTT-2026-33-0007-The-OLE-Vortex-Laminar-Bypass- POC Details
6 CVE-2026-21509 is a critical bypass in the Microsoft Office OLE (Object Linking and Embedding) validation engine. While standard "laminar" exploits attempt to manipulate static COM objects, this repository utilizes Theorem 4.2 to achieve a speculative race-condition bypass of the Object Definition Rule (ODR). https://github.com/SimoesCTT/CTT-MICROSOFT-OFFICE-OLE-MANIFOLD-BYPASS-CVE-2026-21509 POC Details
7 YARA rule and python script to detect potential exploits for the CVE-2026-21509 vulnerability in MS Office https://github.com/decalage2/detect_CVE-2026-21509 POC Details
8 None https://github.com/kaizensecurity/CVE-2026-21509 POC Details
9 CVE-2026-21509 Mitigation https://github.com/planetoid/cve-2026-21509-mitigation POC Details
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III. Intelligence Information for CVE-2026-21509

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IV. Related Vulnerabilities

Same product: Microsoft 365 Apps for Enterprise
Same vendor: Microsoft
Same weakness: CWE-807

V. Comments for CVE-2026-21509

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