CVE-2026-21509

CRITICALPre-NVD 7.89.0▲
EchelonGraph scoreHIGH confidence

Score elevated to 9.0 because this CVE is listed on the CISA Known Exploited Vulnerabilities catalog (added 2026-01-26), indicating real-world exploitation has been confirmed by US federal agencies. the CNA's CVSS baseline 7.8 retained for reference (NVD's own analysis pending). Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, cna:microsoft, epss, ghsa
Trending — 5 sources updated this weekExploited in the wild
9.0EG
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS PROB: 73%CVSS: 7.8Exploit: cisa kev · ssvc active · epss top5pct · epss high · public exploitExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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

CVSS v3
7.8
EG Score
9.0(high)
EG Risk
81(Attend)
EG Risk 81/100SSVC: Attend

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity90% × 45%
Exploitation100% × 40%
Automatability0% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
73%
EPSS %ILE
99%
KEV
⚠ Exploited

Published

January 26, 2026

Last Modified

July 30, 2026

Advisory Details (4)

Auto-updated Jun 4, 2026
⚠️ Active exploitation confirmed. Patch available. Sources: microsoft, cisa.
cisa Patch Available🔴 Active Exploitation

Known Exploited Vulnerabilities Catalog | CISA

Known Exploited Vulnerabilities Catalog | CISA. Listed in CISA Known Exploited Vulnerabilities catalog.

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509
generic🔴 Active Exploitation

CVE-2026-21509 Mitigation Script - Microsoft Office Security Feature Bypass Vulnerability - vsociety

https://www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerability
generic🔴 Active Exploitation

CVE-2026-21509 Detection Script - Microsoft Office Security Feature Bypass Vulnerability - vsociety

https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerability
microsoft Patch Available

Security Update Guide - Microsoft Security Response Center

Security Update Guide - Microsoft Security Response Center. Patch available via Microsoft Security Update

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509

Vendor Advisories for CVE-2026-21509(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 94× in last 7d / 387× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 1,371 total refreshes for this CVE.

  1. 2026-09-19 12:49 UTCVendor advisory
  2. 2026-09-19 12:49 UTCGHSA enrichment
  3. 2026-09-19 08:37 UTCVendor advisory
  4. 2026-09-19 08:37 UTCGHSA enrichment
  5. 2026-09-19 04:24 UTCVendor advisory
  6. 2026-09-19 04:24 UTCGHSA enrichment
  7. 2026-09-19 00:13 UTCVendor advisory
  8. 2026-09-19 00:13 UTCGHSA enrichment
  9. 2026-09-18 20:02 UTCEG score recompute
  10. 2026-09-18 20:02 UTCVendor advisory
  11. 2026-09-18 20:02 UTCGHSA enrichment
  12. 2026-09-18 19:27 UTCEPSS rescore
  13. 2026-09-18 19:20 UTCCISA KEV update
  14. 2026-09-18 15:51 UTCVendor advisory
  15. 2026-09-18 15:51 UTCGHSA enrichment
  16. 2026-09-18 14:15 UTCCISA KEV update
  17. 2026-09-18 11:38 UTCVendor advisory
  18. 2026-09-18 11:38 UTCGHSA enrichment
  19. 2026-09-18 07:27 UTCVendor advisory
  20. 2026-09-18 07:27 UTCGHSA enrichment
  21. 2026-09-18 03:16 UTCVendor advisory
  22. 2026-09-18 03:16 UTCGHSA enrichment
  23. 2026-09-17 23:05 UTCEG score recompute
  24. 2026-09-17 23:05 UTCVendor advisory
  25. 2026-09-17 23:05 UTCGHSA enrichment
Show 75 more
  1. 2026-09-17 18:53 UTCVendor advisory
  2. 2026-09-17 18:52 UTCGHSA enrichment
  3. 2026-09-17 14:40 UTCVendor advisory
  4. 2026-09-17 14:40 UTCGHSA enrichment
  5. 2026-09-17 10:29 UTCVendor advisory
  6. 2026-09-17 10:29 UTCGHSA enrichment
  7. 2026-09-17 06:17 UTCVendor advisory
  8. 2026-09-17 06:17 UTCGHSA enrichment
  9. 2026-09-17 02:04 UTCVendor advisory
  10. 2026-09-17 02:04 UTCGHSA enrichment
  11. 2026-09-16 21:53 UTCVendor advisory
  12. 2026-09-16 21:53 UTCGHSA enrichment
  13. 2026-09-16 17:41 UTCEG score recompute
  14. 2026-09-16 17:41 UTCVendor advisory
  15. 2026-09-16 17:41 UTCGHSA enrichment
  16. 2026-09-16 14:10 UTCCISA KEV update
  17. 2026-09-16 14:07 UTCEPSS rescore
  18. 2026-09-16 13:29 UTCVendor advisory
  19. 2026-09-16 13:28 UTCGHSA enrichment
  20. 2026-09-16 09:15 UTCEG score recompute
  21. 2026-09-16 09:15 UTCVendor advisory
  22. 2026-09-16 09:15 UTCGHSA enrichment
  23. 2026-09-16 05:15 UTCEPSS rescore
  24. 2026-09-16 05:03 UTCVendor advisory
  25. 2026-09-16 05:03 UTCGHSA enrichment
  26. 2026-09-16 00:52 UTCVendor advisory
  27. 2026-09-16 00:52 UTCGHSA enrichment
  28. 2026-09-15 20:41 UTCVendor advisory
  29. 2026-09-15 20:41 UTCGHSA enrichment
  30. 2026-09-15 16:30 UTCVendor advisory
  31. 2026-09-15 16:29 UTCGHSA enrichment
  32. 2026-09-15 12:18 UTCVendor advisory
  33. 2026-09-15 12:18 UTCGHSA enrichment
  34. 2026-09-15 08:06 UTCVendor advisory
  35. 2026-09-15 08:06 UTCGHSA enrichment
  36. 2026-09-15 03:54 UTCEG score recompute
  37. 2026-09-15 03:54 UTCVendor advisory
  38. 2026-09-15 03:54 UTCGHSA enrichment
  39. 2026-09-14 23:43 UTCVendor advisory
  40. 2026-09-14 23:43 UTCGHSA enrichment
  41. 2026-09-14 19:32 UTCVendor advisory
  42. 2026-09-14 19:32 UTCGHSA enrichment
  43. 2026-09-14 19:24 UTCCISA KEV update
  44. 2026-09-14 15:20 UTCVendor advisory
  45. 2026-09-14 15:20 UTCGHSA enrichment
  46. 2026-09-14 11:09 UTCVendor advisory
  47. 2026-09-14 11:09 UTCGHSA enrichment
  48. 2026-09-14 06:58 UTCVendor advisory
  49. 2026-09-14 06:58 UTCGHSA enrichment
  50. 2026-09-14 02:47 UTCVendor advisory
  51. 2026-09-14 02:47 UTCGHSA enrichment
  52. 2026-09-13 22:36 UTCVendor advisory
  53. 2026-09-13 22:36 UTCGHSA enrichment
  54. 2026-09-13 18:25 UTCVendor advisory
  55. 2026-09-13 18:25 UTCGHSA enrichment
  56. 2026-09-13 14:14 UTCVendor advisory
  57. 2026-09-13 14:14 UTCGHSA enrichment
  58. 2026-09-13 10:03 UTCVendor advisory
  59. 2026-09-13 10:03 UTCGHSA enrichment
  60. 2026-09-13 05:51 UTCVendor advisory
  61. 2026-09-13 05:51 UTCGHSA enrichment
  62. 2026-09-13 01:40 UTCVendor advisory
  63. 2026-09-13 01:40 UTCGHSA enrichment
  64. 2026-09-12 21:28 UTCVendor advisory
  65. 2026-09-12 21:28 UTCGHSA enrichment
  66. 2026-09-12 17:16 UTCEG score recompute
  67. 2026-09-12 17:16 UTCVendor advisory
  68. 2026-09-12 17:16 UTCGHSA enrichment
  69. 2026-09-12 15:01 UTCEPSS rescore
  70. 2026-09-12 13:05 UTCVendor advisory
  71. 2026-09-12 13:05 UTCGHSA enrichment
  72. 2026-09-12 08:53 UTCVendor advisory
  73. 2026-09-12 08:53 UTCGHSA enrichment
  74. 2026-09-12 04:41 UTCVendor advisory
  75. 2026-09-12 04:41 UTCGHSA enrichment

Publicly available exploits

(7 references)

Working exploit code is in the public domain (7 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCsuuhm/CVE-2026-21509-handler
    First seen Mar 1, 2026

    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.

    Open source ↗
  • GitHub PoCdecalage2/detect_CVE-2026-21509
    First seen Feb 4, 2026

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

    Open source ↗
  • GitHub PoCSimoesCTT/CTT-MICROSOFT-OFFICE-OLE-MANIFOLD-BYPASS-CVE-2026-21509
    First seen Feb 1, 2026

    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).

    Open source ↗
  • GitHub PoCSimoesCTT/CTT-NFS-Vortex-RCE
    First seen Jan 31, 2026

    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`).

    Open source ↗
  • GitHub PoCgavz/CVE-2026-21509-PoC
    First seen Jan 29, 2026

    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.

    Open source ↗
  • GitHub PoCksk-itdk/KSK-ITDK-CVE-2026-21509-Mitigation
    First seen Jan 29, 2026

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

    Open source ↗
  • GitHub PoCkimstars/Ashwesker-CVE-2026-21509
    First seen Jan 27, 2026

    CVE-2026-21509

    Open source ↗

Frequently asked(6)

What is CVE-2026-21509?
CVE-2026-21509 is a critical vulnerability published on January 26, 2026. Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
When was CVE-2026-21509 disclosed?
CVE-2026-21509 was first published in the National Vulnerability Database on January 26, 2026, with the most recent update on July 30, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-21509 actively exploited?
Yes. CISA added CVE-2026-21509 to the Known Exploited Vulnerabilities catalog on January 26, 2026, affecting Microsoft Office. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.
What is the CVSS score of CVE-2026-21509?
CVE-2026-21509 has a CVSS v4.0 base score of 7.8 (CNA self-assessment; NVD's own analysis pending). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.
Which products are affected by CVE-2026-21509?
CVE-2026-21509 affects Microsoft Office. The full affected-products list, including version ranges and fixed versions, is shown in the Affected Packages section of this page.
How do I remediate CVE-2026-21509?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-21509, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2026-21509

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