Microsoft Office Security Feature Bypass Vulnerability
Microsoft — Microsoft 365 Apps for Enterprise
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
7.8
72.6%
Vector breakdown
- 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
- Published
- Jan 26, 2026
- Modified
- Jun 25, 2026
- Added to KEV
- Jan 26, 2026
- Federal patch due
- Feb 16, 2026
CISA 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.
Weakness classification
Affected packages
Proof-of-concept & exploitation references
8 foundWeaponization
Public repositories whose name or description references CVE-2026-21509, found via a live GitHub search at request time. These are community-sourced signals, not a verified working exploit - cross-check each one before relying on it, and treat higher star counts and recent activity as (weak) corroboration, not proof.
- gavz/CVE-2026-21509-PoC★ 20
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.
updated Jul 23, 2026
- kimstars/Ashwesker-CVE-2026-21509★ 11
CVE-2026-21509
updated Jul 16, 2026
- suuhm/CVE-2026-21509-handler★ 8
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.
updated Jul 13, 2026
- SimoesCTT/CTT-MICROSOFT-OFFICE-OLE-MANIFOLD-BYPASS-CVE-2026-21509★ 3
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).
updated Feb 10, 2026
- decalage2/detect_CVE-2026-21509★ 3
YARA rule and python script to detect potential exploits for the CVE-2026-21509 vulnerability in MS Office
updated Feb 21, 2026
- SimoesCTT/CTT-NFS-Vortex-RCE★ 3
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`).
updated Feb 8, 2026
- ksk-itdk/KSK-ITDK-CVE-2026-21509-Mitigation★ 2
Powershell script with Detection and Remediation for CVE-2026-21509
updated May 11, 2026
- SimoesCTT/SCTT-2026-33-0007-The-OLE-Vortex-Laminar-Bypass-★ 1
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.
updated Jan 31, 2026
References
Frequently asked questions
What is CVE-2026-21509?
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
How severe is CVE-2026-21509?
CVE-2026-21509 has a CVSS base score of 7.8 out of 10 (CVSS 3.1).
Is CVE-2026-21509 actively exploited in the wild?
Yes. CVE-2026-21509 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added Jan 26, 2026, meaning CISA has confirmed evidence of active exploitation.
What is the EPSS score for CVE-2026-21509?
72.6% - meaning FIRST.org's EPSS model estimates a 72.6% probability this vulnerability will be exploited in the wild within 30 days (99% percentile among all scored CVEs).
Is there exploit tooling available for CVE-2026-21509?
We found 8 public GitHub repositories referencing CVE-2026-21509, though none matched a known Nuclei template or Metasploit module at last check. Review each one before relying on it - see the proof-of-concept section above.
What type of vulnerability is CVE-2026-21509?
CVE-2026-21509 is classified under CWE-807 (CWE-807: Reliance on Untrusted Inputs in a Security Decision).
Cross-checked against
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