KEV Intelligence

Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2026-21509

Microsoft Office Security Feature Bypass Vulnerability

Microsoft / Microsoft 365 Apps for Enterprise · affected before https://aka.ms/OfficeSecurityReleases

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Severity
CVSS 7.8 · High
Confidence
Confirmed
Exploit status
Exploited in the wild
EPSS
72.2%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2026-21509 is an unauthenticated Microsoft Office Security Feature Bypass Vulnerability affecting Microsoft Microsoft 365 Apps for Enterprise and 4 other products. Reliance on untrusted inputs in a security...

Is it exploited?

Yes. KEV Intelligence tracks this CVE as a known exploited vulnerability. Confidence is confirmed.

Who is affected?

Microsoft / Microsoft 365 Apps for Enterprise affected before https://aka.ms/officesecurityreleases.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

Microsoft Office Security Feature Bypass Vulnerability

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

Vendor Product Affected Status
Microsoft Microsoft 365 Apps for Enterprise Before https://aka.ms/OfficeSecurityReleases Affected
Microsoft Microsoft Office 2016 Before 16.0.5539.1001 Affected
Microsoft Microsoft Office 2019 Before 16.0.10417.20095 Affected
Microsoft Microsoft Office LTSC 2021 Before https://aka.ms/OfficeSecurityReleases Affected
Microsoft Microsoft Office LTSC 2024 Before https://aka.ms/OfficeSecurityReleases Affected
View vendor advisory (opens in new tab)
Published
26 Jan 2026
Exploitation Reported
01 Jun 2026
Attack vector
Local
Complexity
Low
Privileges
None
User interaction
Required

Tags

cisa microsoft

CVE References

Exploitation evidence

Why KEV Intelligence marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CVE

Recorded 01 Jun 2026

Independent exploitation attestation added to the KEV Intelligence record.

Proof of concept available

GitHub

Recorded 12 Mar 2026

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the KEV Intelligence Pro API.

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Source Added
CVE First 2026-06-01 10:49 UTC
CISA 2026-06-02 14:03 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
0
User-Agents
0

Raw values available in Pro and Enterprise.

Scanner coverage

No scanner integrations recorded yet.

Virtual patch status

No KEV Intelligence virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

No detection artifacts or sensor request patterns are available for this CVE yet.

Check back as sensor telemetry and scanner integrations are updated.

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

7.8 High
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

EPSS

72.2%

Weaknesses

Reliance on Untrusted Inputs in a Security Decision CWE-807

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

sentinel-aidefense/CVE-2026-21509

github · Created 2026-06-30 16:19:55 UTC · 0 stars

DameDode/CVE-2026-21509-POC

github · Created 2026-03-12 18:59:40 UTC · 0 stars

POC for the Office vulnerability

suuhm/CVE-2026-21509-handler

github · Created 2026-03-01 17:00:37 UTC · 7 stars

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.

decalage2/detect_CVE-2026-21509

github · Created 2026-02-04 14:13:02 UTC · 3 stars

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

SimoesCTT/CTT-MICROSOFT-OFFICE-OLE-MANIFOLD-BYPASS-CVE-2026-21509

github · Created 2026-02-01 17:31:24 UTC · 3 stars

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).

ksk-itdk/KSK-ITDK-CVE-2026-21509-Mitigation

github · Created 2026-01-29 11:40:30 UTC · 2 stars

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

gavz/CVE-2026-21509-PoC

github · Created 2026-01-29 00:51:18 UTC · 17 stars

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.

kimstars/Ashwesker-CVE-2026-21509

github · Created 2026-01-27 12:03:20 UTC · 10 stars

CVE-2026-21509

Timeline

From disclosure to observed exploitation

  1. Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  2. Added to KEV Intelligence KEV Feed

    High-confidence, third-party attested exploitation

  3. Public PoC available

    Public proof-of-concept code published

  4. CVE published

    Vulnerability disclosed publicly

  5. CVE ID reserved

    Identifier reserved by the CNA

Pro API

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Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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GET /api/v2/pro/kevs/CVE-2026-21509

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2026-21509",
  "confidence": "Confirmed",
  "cvss_score": 7.8,
  "epss_score": 0.72152,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}

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