CVE-2026-21509CISA KEV: Actively Exploited

Microsoft Office Security Feature Bypass Vulnerability

Published Jan 26, 2026·Updated Jan 26, 2026

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.

Public Exploits & PoCs13 found

PoC: detect_CVE-2026-21509

YARA rule and python script to detect potential exploits for the CVE-2026-21509 vulnerability in MS Office

1

PoC: CTT-NFS-Vortex-RCE

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`).

1

PoC: CVE-2026-21509-POC

POC for the Office vulnerability

PoC: CVE-2026-21509-handler

PowerShell script to check, apply, and test the Kill-Bit protection for the CVE-2026-21509 Microsoft Office zero-day vulnerability affecting Office 2016/2019/LTSC.

PoC: cve-2026-21509-mitigation

CVE-2026-21509 Mitigation

PoC: CTT-MICROSOFT-OFFICE-OLE-MANIFOLD-BYPASS-CVE-2026-21509

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).

PoC: SCTT-2026-33-0007-The-OLE-Vortex-Laminar-Bypass-

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.

PoC: KSK-ITDK-CVE-2026-21509-Mitigation

Powershell script with Detection and Remediation for CVE-2026-21509

PoC: CVE-2026-21509-PoC

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.

PoC: CVE-2026-21509-PoC

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.

PoC: CVE-2026-21509-PoC

CVE-2026-21509

PoC: Ashwesker-CVE-2026-21509

CVE-2026-21509

PoC: Ashwesker-CVE-2026-21509

CVE-2026-21509

References

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