CVE-2026-21509

HIGH KEV

Microsoft 365 Apps and Office - Security Feature Bypass via Untrusted Input

Title source: llm
STIX 2.1

Exploitation Summary

CVE-2026-21509 is actively exploited and listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added January 26, 2026. EIP tracks 13 public exploits from researchers including XiaomingX, gavz, kimstars.

AI-analyzed exploit summary This repository contains a functional exploit PoC for CVE-2026-21509, leveraging a novel approach combining fluid dynamics theory with NFS protocol exploitation. The code implements a temporal vortex attack using RPC fragmentation and energy cascade techniques to achieve remote code execution.

Description

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

Exploits (13)

github WORKING POC 10 stars
by XiaomingX · pythonpoc
https://github.com/XiaomingX/data-cve-poc-py-v1/tree/main/2026/CVE-2026-21509

This repository contains a functional exploit PoC for CVE-2026-21509, leveraging a novel approach combining fluid dynamics theory with NFS protocol exploitation. The code implements a temporal vortex attack using RPC fragmentation and energy cascade techniques to achieve remote code execution.

Classification
Working Poc 85%
Attack Type
Rce
Complexity
Complex
Reliability
Theoretical
Target: NFS (Network File System) protocol implementation
No auth needed
Prerequisites: Network access to target NFS server · Python environment with required dependencies (numpy)
devstral-2 · analyzed Feb 27, 2026 Full analysis →
nomisec WORKING POC 9 stars
by gavz · poc
https://github.com/gavz/CVE-2026-21509-PoC

This repository provides a harmless, non-exploit Proof of Concept for CVE-2026-21509, a Microsoft Office security feature bypass vulnerability. It generates a harmless DOCX file containing dummy embedded OLE components for defensive research, EDR/AV visibility testing, and training purposes.

Classification
Working Poc 100%
Attack Type
Other
Complexity
Trivial
Reliability
Theoretical
Target: Microsoft Office 2016, 2019, LTSC 2021, LTSC 2024, Microsoft 365 Apps for Enterprise
No auth needed
Prerequisites: User interaction (the victim must open the file)
devstral-2 · analyzed Feb 16, 2026 Full analysis →
nomisec WORKING POC 8 stars
by kimstars · poc
https://github.com/kimstars/Ashwesker-CVE-2026-21509

This is a working PoC for CVE-2026-21509, a Microsoft Office OLE security feature bypass vulnerability. It generates a DOCX file with an embedded OLE object to test the bypass, requiring user interaction to open the file.

Classification
Working Poc 90%
Attack Type
Auth Bypass
Complexity
Moderate
Reliability
Reliable
Target: Microsoft Office 2016, 2019, LTSC 2021, LTSC 2024, Microsoft 365 Apps for Enterprise
No auth needed
Prerequisites: Vulnerable Microsoft Office installation (pre-Jan 26, 2026 patch) · User interaction to open the malicious DOCX file
MITRE ATT&CK
devstral-2 · analyzed Feb 16, 2026 Full analysis →
nomisec WORKING POC 3 stars
by SimoesCTT · poc
https://github.com/SimoesCTT/CTT-MICROSOFT-OFFICE-OLE-MANIFOLD-BYPASS-CVE-2026-21509

This repository contains a proof-of-concept exploit for CVE-2026-21509, leveraging a temporal resonance technique to bypass Microsoft Office OLE validation. The exploit uses a 33-layer manifold to achieve speculative execution, evading detection mechanisms like AMSI/EDR.

Classification
Working Poc 85%
Attack Type
Rce
Complexity
Complex
Reliability
Theoretical
Target: Microsoft Office (OLE validation engine)
No auth needed
Prerequisites: Python environment · Target system with vulnerable Microsoft Office installation
devstral-2 · analyzed Feb 16, 2026 Full analysis →
nomisec WORKING POC 3 stars
by SimoesCTT · poc
https://github.com/SimoesCTT/CTT-NFS-Vortex-RCE

This PoC exploits a vulnerability in NFS (CVE-2026-21509) using a novel approach based on fluid dynamics (CTT-Navier-Stokes mapping) to craft RPC fragments. It implements Theorem 4.2 energy cascade for evasion and payload delivery, targeting NFS protocol procedures.

Classification
Working Poc 85%
Attack Type
Rce
Complexity
Complex
Reliability
Theoretical
Target: NFS (Network File System) protocol implementation (version not specified)
No auth needed
Prerequisites: Network access to target NFS service (port 2049) · Vulnerable NFS implementation · Python environment with required dependencies (numpy)
devstral-2 · analyzed Feb 16, 2026 Full analysis →
nomisec SCANNER 2 stars
by decalage2 · poc
https://github.com/decalage2/detect_CVE-2026-21509

This repository provides a YARA rule and a Python script to detect MS Office files containing 'Shell.Explorer.1' OLE objects, which are indicators of potential exploitation of CVE-2026-21509. The script analyzes OpenXML, OLE/CFB, and RTF documents for the presence of the specific CLSID associated with the vulnerability.

Classification
Scanner 100%
Attack Type
Other
Complexity
Moderate
Reliability
Reliable
Target: Microsoft Office
No auth needed
Prerequisites: Access to potentially malicious MS Office files
devstral-2 · analyzed Feb 16, 2026 Full analysis →
nomisec WORKING POC 1 stars
by SimoesCTT · poc
https://github.com/SimoesCTT/SCTT-2026-33-0007-The-OLE-Vortex-Laminar-Bypass-

This PoC exploits CVE-2026-21509 by bypassing OLE/COM mitigations in Microsoft Office via a 33-layer energy cascade technique, achieving RCE through temporal resonance manipulation in OLE2 objects.

Classification
Working Poc 90%
Attack Type
Rce
Complexity
Complex
Reliability
Theoretical
Target: Microsoft Office 2016-2024 / Microsoft 365
No auth needed
Prerequisites: Victim must open a malicious Office document
devstral-2 · analyzed Feb 16, 2026 Full analysis →
nomisec SCANNER 1 stars
by ksk-itdk · poc
https://github.com/ksk-itdk/KSK-ITDK-CVE-2026-21509-Mitigation

This repository contains PowerShell scripts for detecting and remediating CVE-2026-21509 by checking and setting registry values related to Microsoft Office COM compatibility. It does not include exploit code but provides mitigation steps.

Classification
Scanner 90%
Attack Type
Other
Complexity
Trivial
Reliability
Reliable
Target: Microsoft Office (ClickToRun)
Auth required
Prerequisites: Administrative access to modify registry values
devstral-2 · analyzed Feb 16, 2026 Full analysis →
github WORKING POC
by XZ1r0 · pythonpoc
https://github.com/XZ1r0/cve-2026-poc-collection/tree/main/windows/CVE-2026-21509-PoC

This repository contains a functional PoC for CVE-2026-21509, a Microsoft Office security feature bypass vulnerability. The PoC generates a harmless DOCX file with dummy OLE components to simulate structural markers related to the vulnerability, useful for defensive research and EDR/AV visibility testing.

Classification
Working Poc 95%
Attack Type
Auth Bypass
Complexity
Moderate
Reliability
Reliable
Target: Microsoft Office (2016, 2019, LTSC 2021, LTSC 2024, Microsoft 365 Apps for Enterprise)
No auth needed
Prerequisites: User interaction (victim must open the crafted DOCX file)
devstral-2 · analyzed May 21, 2026 Full analysis →
nomisec WORKING POC
by DameDode · client-side
https://github.com/DameDode/CVE-2026-21509-POC

The repository contains a functional Python script that generates a malicious DOCX file exploiting CVE-2026-21509 by embedding a crafted OLE compound file with a user-specified CLSID. The script constructs a valid Office Open XML document with required metadata and relationships.

Classification
Working Poc 95%
Attack Type
Rce
Complexity
Moderate
Reliability
Reliable
Target: Microsoft Office Word (specific version not specified)
No auth needed
Prerequisites: Python 3.6+ · valid CLSID for exploitation
devstral-2 · analyzed Mar 13, 2026 Full analysis →
nomisec WORKING POC
by suuhm · poc
https://github.com/suuhm/CVE-2026-21509-handler

This PowerShell script applies a kill-bit registry modification to mitigate CVE-2026-21509 in Microsoft Office 2016 by disabling a vulnerable COM object. It includes functionality to check, apply, and remove the kill-bit, as well as verify relevant KB updates.

Classification
Working Poc 95%
Attack Type
Other
Complexity
Trivial
Reliability
Reliable
Target: Microsoft Office 2016 (32/64-bit)
Auth required
Prerequisites: Administrator privileges · Microsoft Office 2016 installed
devstral-2 · analyzed Mar 02, 2026 Full analysis →
nomisec WORKING POC
by planetoid · poc
https://github.com/planetoid/cve-2026-21509-mitigation

This repository contains a PowerShell script that mitigates CVE-2026-21509, a Microsoft Office Security Feature Bypass Vulnerability, by applying registry keys to block a vulnerable COM component. The script detects Office installation types and applies the necessary registry changes to prevent exploitation.

Classification
Working Poc 95%
Attack Type
Other
Complexity
Moderate
Reliability
Reliable
Target: Microsoft Office 2016 and 2019
Auth required
Prerequisites: Administrative privileges · Microsoft Office 2016 or 2019 installed
devstral-2 · analyzed Feb 16, 2026 Full analysis →
nomisec WORKING POC
by kaizensecurity · poc
https://github.com/kaizensecurity/CVE-2026-21509

The repository contains a Windows shortcut (LNK) file that exploits CVE-2026-21509 by executing 'calc.exe' via a crafted path. This is a functional PoC demonstrating arbitrary code execution through a malicious LNK file.

Classification
Working Poc 90%
Attack Type
Rce
Complexity
Trivial
Reliability
Reliable
Target: Windows (version unspecified)
No auth needed
Prerequisites: Victim interaction (e.g., opening the LNK file)
devstral-2 · analyzed Feb 16, 2026 Full analysis →

Scores

CVSS v3 7.8
EPSS 0.0794
EPSS Percentile 92.3%
Attack Vector LOCAL
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CISA SSVC

Vulnrichment
Exploitation active
Automatable no
Technical Impact total

Details

CISA KEV 2026-01-26
VulnCheck KEV 2026-01-26
ENISA EUVD EUVD-2026-4666
CWE
CWE-807
Status published
Products (10)
microsoft/365_apps (2 CPE variants)
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
microsoft/office 2016 (2 CPE variants)
microsoft/office 2019 (2 CPE variants)
microsoft/office_long_term_servicing_channel 2021 (2 CPE variants)
microsoft/office_long_term_servicing_channel 2024 (2 CPE variants)
Published Jan 26, 2026
KEV Added Jan 26, 2026
Tracked Since Feb 18, 2026