CVE-2026-21509

HIGHPre-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. a secondary CVSS source baseline 7.8 retained for reference (NVD's own analysis pending). Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, epss, ghsa, secondary
Trending — 5 sources updated this weekExploited in the wild
7.8
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS: 72%CVSS: 7.8Exploit: NoneExposed: 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
99.4%
KEV
⚠ Exploited

Published

January 26, 2026

Last Modified

June 25, 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 82× in last 7d / 371× 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 663 total refreshes for this CVE.

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

Frequently asked(6)

What is CVE-2026-21509?
CVE-2026-21509 is a high 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 June 25, 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 v3 base score of 7.8 (NVD). 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.

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