CVE-2026-66809

MEDIUMNVD 5.55.5—
EchelonGraph scoreMEDIUM confidence

Score 5.5 from GitHub Security Advisory published 2026-08-11. NVD baseline CVSS 5.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Trending — 4 sources updated this week
5.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.4%CVSS: 5.5Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Out-of-bounds read in Microsoft Office allows an unauthorized attacker to disclose information locally.

CVSS v3
5.5
EG Score
5.5MEDIUMmedium confidence
EG Risk
25
EG Risk 25/100CISA SSVC

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
Severity55% × 45%
Exploitation0% × 40%
Automatability0% × 15%
CISA SSVC: Track at every mission impact level.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.4%
EPSS %ILE
35th
KEV
Not listed

CISA SSVCTrack at every mission impact level.

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

August 11, 2026

Last Modified

September 29, 2026

Advisory Details (1)

Auto-updated Aug 11, 2026
Patch available. Sources: microsoft.
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-2026-66809

Vendor Advisories for CVE-2026-66809(2)

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 19× in last 7d / 105× 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 289 total refreshes for this CVE.

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

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-66809?
CVE-2026-66809 is a medium vulnerability published on August 11, 2026. Out-of-bounds read in Microsoft Office allows an unauthorized attacker to disclose information locally.
When was CVE-2026-66809 disclosed?
CVE-2026-66809 was first published on August 11, 2026, with the most recent update on September 29, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-66809 actively exploited?
CVE-2026-66809 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.4% probability of exploitation in the next 30 days (35th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-66809?
CVE-2026-66809 has a CVSS v3 base score of 5.5 (NVD).
How do I remediate CVE-2026-66809?
A fix for CVE-2026-66809 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-66809 are linked in the Vendor Advisories panel on this page.

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