CVE-2026-84140

CRITICALNVD 9.89.8—
EchelonGraph scoreHIGH confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2026-09-01. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Trending — 3 sources updated this week
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.8Exploit: None knownExposed: 0

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

Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.

CVSS v3
9.8
EG Score
9.8(high)
EG Risk
59(Track)
EG Risk 59/100SSVC: Track

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
Severity98% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
8%
KEV
Not listed

Published

September 1, 2026

Last Modified

September 3, 2026

Advisory Details (5)

Auto-updated Sep 17, 2026
No patch confirmed yet.
generic

Security Vulnerabilities fixed in Thunderbird 153.2 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-88/
generic

Security Vulnerabilities fixed in Thunderbird 155 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-86/
generic

Security Vulnerabilities fixed in Firefox ESR 153.2 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-85/
generic

Security Vulnerabilities fixed in Firefox 155 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-82/
generic

Access Denied

https://bugzilla.mozilla.org/show_bug.cgi?id=2063780

Vendor Advisories for CVE-2026-84140(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 50× in last 7d / 130× 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 130 total refreshes for this CVE.

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

Frequently asked(5)

What is CVE-2026-84140?
CVE-2026-84140 is a critical vulnerability published on September 1, 2026. Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.
When was CVE-2026-84140 disclosed?
CVE-2026-84140 was first published in the National Vulnerability Database on September 1, 2026, with the most recent update on September 3, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-84140 actively exploited?
CVE-2026-84140 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 91.9% of all scored CVEs.
What is the CVSS score of CVE-2026-84140?
CVE-2026-84140 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2026-84140?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-84140, 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

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