CVE-2026-84142

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.

Internally found bugs present in Thunderbird 154. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155 and Thunderbird 155.

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
23%
KEV
Not listed

Published

September 1, 2026

Last Modified

September 3, 2026

Advisory Details (4)

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

Security Vulnerabilities fixed in Thunderbird 155 — Mozilla

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

Security Vulnerabilities fixed in Firefox 155 — Mozilla

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

Client Challenge

https://bugzilla.mozilla.org/buglist.cgi?bug_id=2048796%2C2053150%2C2057356
generic

Client Challenge

https://bugzilla.mozilla.org/buglist.cgi?bug_id=2029421%2C2040889%2C2045313%2C2045435%2C2053578%2C2058621%2C2058626

Vendor Advisories for CVE-2026-84142(1)

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

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 53× in last 7d / 139× 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 139 total refreshes for this CVE.

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

Related CVEs

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Frequently asked(5)

What is CVE-2026-84142?
CVE-2026-84142 is a critical vulnerability published on September 1, 2026. Internally found bugs present in Thunderbird 154. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155 and Thunderbird 155.
When was CVE-2026-84142 disclosed?
CVE-2026-84142 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-2026-84142 actively exploited?
CVE-2026-84142 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 76.6% of all scored CVEs.
What is the CVSS score of CVE-2026-84142?
CVE-2026-84142 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2026-84142?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-84142, 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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