CVE-2026-21509
Confirmed PUBLISHEDMicrosoft Office Security Feature Bypass Vulnerability
1 day faster than CISA KEV
Recommended Action
Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.
At a Glance
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
- CVE Published
- Jan 26, 2026
- Exploitation Reported
- Jun 01, 2026
- CVSS
- 7.8 High
- EPSS
- 72.2%
Affected Versions
| Vendor | Product | Version | Status |
|---|---|---|---|
| Microsoft |
Microsoft 365 Apps for Enterprise
|
16.0.1 to < https://aka.ms/OfficeSecurityReleases |
Affected |
| Microsoft |
Microsoft Office 2016
|
16.0.0 to < 16.0.5539.1001 |
Affected |
| Microsoft |
Microsoft Office 2019
|
19.0.0 to < 16.0.10417.20095 |
Affected |
| Microsoft |
Microsoft Office LTSC 2021
|
16.0.1 to < https://aka.ms/OfficeSecurityReleases |
Affected |
| Microsoft |
Microsoft Office LTSC 2024
|
16.0.0 to < https://aka.ms/OfficeSecurityReleases |
Affected |
CVE References
- Microsoft Office Security Feature Bypass Vulnerability msrc.microsoft.com · Vendor Advisory https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509
Recommended Actions
- Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.
- Check enrichment artifacts for scanner coverage and available PoCs before rolling remediation validation.
- Use the Pro API to automate enrichment, telemetry, and workflow delivery for VM, SOC, and CTI pipelines.
Known Exploited Vulnerability Sources
Catalogues that list this CVE as a known exploited vulnerability.
Per-source evidence links for KEV attestations are available through the KEVIntel Pro API.
Learn about Pro API access| Source | Added |
|---|---|
| CVE First | 2026-06-01 10:49 UTC |
| CISA | 2026-06-02 14:03 UTC |
No detection artifacts or sensor request patterns are available for this CVE yet.
Check back as sensor telemetry and scanner integrations are updated.
Virtual Patch
Compensating WAF rules to help reduce exposure to this CVE. Rule content and deployable vendor exports are available with KEVIntel Enterprise.
KEVIntel does not currently have a virtual patch for this CVE. When available, KEVIntel virtual patches ship as deployable ModSecurity, Cloudflare, and AWS WAF rules.
Enterprise feature. Virtual patch rule content and deployable vendor exports (ModSecurity, Cloudflare, AWS WAF) are available to KEVIntel Enterprise users.
CVSS Scores
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
Exploitation Status
Exploited in the wild
Recorded 2026-06-01 10:49:49 UTC · CVE
Proof of concept available
Recorded 2026-03-12 18:59:40 UTC · GitHub
Weaknesses (CWE)
-
Reliance on Untrusted Inputs in a Security Decision
Potential Proof of Concepts
These PoCs are unverified and could contain malware. Use at your own risk.
github · Created 2026-06-30 16:19:55 UTC · 0 stars
github · Created 2026-03-12 18:59:40 UTC · 0 stars
POC for the Office vulnerability
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.
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
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).
github · Created 2026-01-29 11:40:30 UTC · 2 stars
Powershell script with Detection and Remediation for CVE-2026-21509
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.
github · Created 2026-01-27 12:03:20 UTC · 10 stars
CVE-2026-21509
Timeline
Key exploitation, disclosure, scanner coverage, and KEV attestation events for this CVE.
-
14:03 UTC about 2 months ago14:03 UTC · about 2 months ago
Added to CISA KEV
Listed in the CISA Known Exploited Vulnerabilities catalog
-
10:49 UTC about 2 months ago10:49 UTC · about 2 months ago
Added to KEVIntel KEV Feed
High-confidence, third-party attested exploitation
-
12:03 UTC 6 months ago12:03 UTC · 6 months ago
Public PoC available
Public proof-of-concept code published
-
17:06 UTC 6 months ago17:06 UTC · 6 months ago
CVE published
Vulnerability disclosed publicly
-
18:10 UTC 7 months ago18:10 UTC · 7 months ago
CVE ID reserved
Identifier reserved by the CNA
Automate This Intelligence with the Pro API
Confidence scoring, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.
Pro API Example
GET /api/v2/pro/kevs/CVE-2026-21509
{
"cve_id": "CVE-2026-21509",
"title": "Microsoft Office Security Feature Bypass Vulnerability",
"affected_vendor": "Microsoft",
"affected_product": "Microsoft 365 Apps for Enterprise, Microsoft Office 2016, Microsoft Office 2019, Microsoft Office LTSC 2021, Microsoft Office LTSC 2024",
"affected_versions": [
{ "vendor": "...", "product": "...", "status": "affected", "display_label": "..." }
],
"confidence": "Confirmed",
"cvss_score": 7.8,
"epss_score": 0.72152,
"exploit_status": {
"exploited_in_the_wild": true,
"active_exploitation_observed": false
},
"sensor_telemetry": { "...": "Pro API fields" },
"proof_of_concepts": [ "..." ],
"scanner_integrations": [ "..." ]
}