CVE-2026-84639

CRITICALPre-NVD 9.19.1—
EchelonGraph scoreHIGH confidence

Score 9.1 from GitHub Security Advisory (severity: CRITICAL) published 2026-09-02. CISA-ADP (Vulnrichment) CVSS v3.1 baseline 9.1; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: cisa-adp, epss, ghsa
Trending — 3 sources updated this week
9.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.1Exploit: None knownExposed: 0

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

Triggering an error condition in certain MIME bodies would cause uninitialized memory to be used. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

CVSS v3
9.1
EG Score
9.1(high)
EG Risk
56(Track)
EG Risk 56/100SSVC: 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
Severity91% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
26%
KEV
Not listed

Published

September 1, 2026

Last Modified

September 17, 2026

Advisory Details (4)

Auto-updated Sep 15, 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 140.15 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-87/
generic

Security Vulnerabilities fixed in Thunderbird 155 — Mozilla

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

Access Denied

https://bugzilla.mozilla.org/show_bug.cgi?id=2061087

Vendor Advisories for CVE-2026-84639(1)

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

Affected Packages

(3 across 3 ecosystems)
Debian:12(1)
PackageVulnerable rangeFixed inDependents
thunderbird1:102.11.0-1 ... 1:140.9.1esr-1~deb13u1 (227 versions)1:140.15.0esr-1~deb12u1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
thunderbird1:128.13.0esr-1 ... 1:140.9.1esr-1~deb13u1 (83 versions)1:140.15.0esr-1~deb13u1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
thunderbird1:128.13.0esr-1 ... 1:153.2.0esr-1 (93 versions)——

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 53× in last 7d / 133× 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 133 total refreshes for this CVE.

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

Frequently asked(5)

What is CVE-2026-84639?
CVE-2026-84639 is a critical vulnerability published on September 1, 2026. Triggering an error condition in certain MIME bodies would cause uninitialized memory to be used. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
When was CVE-2026-84639 disclosed?
CVE-2026-84639 was first published in the National Vulnerability Database on September 1, 2026, with the most recent update on September 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-84639 actively exploited?
CVE-2026-84639 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 74.5% of all scored CVEs.
What is the CVSS score of CVE-2026-84639?
CVE-2026-84639 has a CVSS v3.1 base score of 9.1 (CISA-ADP / Vulnrichment enrichment; NVD's own analysis pending).
How do I remediate CVE-2026-84639?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-84639, 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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