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

Executive Summary

Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

Overview

7.8

CVSS HIGH

Important

MS Severity

Exploited

MS Exploit Status

Exploitation Detected

MS Exploit Likelihood

Category Security Feature Bypass

Weakness CWE-807: Reliance on Untrusted Inputs in a Security Decision

Released Jan 13 2026

Last Updated Jan 13 2026

Publicly Disclosed No

CISA KEV Listed (added 2026-01-26)

Known Exploits None Known

EPSS Score 0.72152 — 0.99379 percentile

NVD CVSS 7.8 HIGH — matches MSRC

CVSS Vector

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

EXPLOIT CODE MATURITY

Functional

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 7.2

EPSS Score

0.72152

probability of exploitation in the next 30 days

0.99379 percentile - updated 2026-08-14

View on FIRST.org

Affected Products

10 affected products

Product	KB Article	Severity	Impact	Restart Required
Microsoft 365 Apps for Enterprise for 32-bit Systems	`Click to Run (Security Update)`	Important	Security Feature Bypass	No
Microsoft 365 Apps for Enterprise for 64-bit Systems	`Click to Run (Security Update)`	Important	Security Feature Bypass	No
Microsoft Office 2016 (32-bit edition)	`5002713 (Security Update)`	Important	Security Feature Bypass	Maybe
Microsoft Office 2016 (64-bit edition)	`5002713 (Security Update)`	Important	Security Feature Bypass	Maybe
Microsoft Office 2019 for 32-bit editions	`Click to Run (Security Update)`	Important	Security Feature Bypass	No
Microsoft Office 2019 for 64-bit editions	`Click to Run (Security Update)`	Important	Security Feature Bypass	No
Microsoft Office LTSC 2021 for 32-bit editions	`Click to Run (Security Update)`	Important	Security Feature Bypass	No
Microsoft Office LTSC 2021 for 64-bit editions	`Click to Run (Security Update)`	Important	Security Feature Bypass	No
Microsoft Office LTSC 2024 for 32-bit editions	`Click to Run (Security Update)`	Important	Security Feature Bypass	No
Microsoft Office LTSC 2024 for 64-bit editions	`Click to Run (Security Update)`	Important	Security Feature Bypass	No

Patches

2 patches

Article	Type	Restart
`Click to Run`	Security Update	No
`5002713`	Security Update	Maybe

Exploits & PoC

13 public PoCs

Unverified third-party code

Public proof-of-concept repositories aggregated from PoC-in-GitHub. They are not reviewed and may be incomplete, non-functional, or malicious — inspect the code before running anything.

Repository	Stars	Published	Description
gavz/CVE-2026-21509-PoC	20	2026-01-29	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; se
kimstars/Ashwesker-CVE-2026-21509	11	2026-01-27	CVE-2026-21509
suuhm/CVE-2026-21509-handler	8	2026-03-01	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.
SimoesCTT/CTT-NFS-Vortex-RCE	3	2026-01-31	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`).
SimoesCTT/CTT-MICROSOFT-OFFICE-OLE-MANIFOLD-BYPASS-CVE-2026-21509	3	2026-02-01	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 repos
decalage2/detect_CVE-2026-21509	3	2026-02-04	YARA rule and python script to detect potential exploits for the CVE-2026-21509 vulnerability in MS Office
ksk-itdk/KSK-ITDK-CVE-2026-21509-Mitigation	2	2026-01-29	Powershell script with Detection and Remediation for CVE-2026-21509
SimoesCTT/SCTT-2026-33-0007-The-OLE-Vortex-Laminar-Bypass-	1	2026-01-31	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" f
kaizensecurity/CVE-2026-21509	0	2026-02-05
planetoid/cve-2026-21509-mitigation	0	2026-02-11	CVE-2026-21509 Mitigation
DameDode/CVE-2026-21509-POC	0	2026-03-12	POC for the Office vulnerability
sentinel-aidefense/CVE-2026-21509	0	2026-06-30	CVE-2026-21509 Research writeup
razureink/cve-2026-21509-office_security_bypass_reproduction	0	2026-07-23	CVE Reproduction: cve-2026-21509-office_security_bypass_reproduction

Detection Rules

No public Sigma or Nuclei detection rule has been mapped to this CVE yet. Coverage is concentrated on exploited / high-profile vulnerabilities; check SigmaHQ for updates.

Acknowledgments

Microsoft Threat Intelligence Center (MSTIC), Microsoft Security Response Center (MSRC), and Office Product Group Security Team
Google Threat Intelligence Group

References

MSRC Advisory MITRE NVD