CVE-2026-84640

HIGHPre-NVD 7.57.5—
EchelonGraph scoreHIGH confidence

Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-09-02. CISA-ADP (Vulnrichment) CVSS v3.1 baseline 7.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: cisa-adp, epss, ghsa
Trending — 3 sources updated this week
7.5EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.5Exploit: None knownExposed: 0

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

A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

CVSS v3
7.5
EG Score
7.5(high)
EG Risk
49(Track)
EG Risk 49/100SSVC: 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
Severity75% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
18%
KEV
Not listed

Published

September 1, 2026

Last Modified

September 3, 2026

Advisory Details (4)

Auto-updated Sep 2, 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=2063964

Vendor Advisories for CVE-2026-84640(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 27× in last 7d / 71× 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.

  1. 2026-09-19 22:22 UTCEG score recompute
  2. 2026-09-19 22:22 UTCGHSA enrichment
  3. 2026-09-19 09:57 UTCGHSA enrichment
  4. 2026-09-18 21:24 UTCEG score recompute
  5. 2026-09-18 21:24 UTCGHSA enrichment
  6. 2026-09-18 19:28 UTCEPSS rescore
  7. 2026-09-18 09:00 UTCGHSA enrichment
  8. 2026-09-17 20:40 UTCEG score recompute
  9. 2026-09-17 20:40 UTCGHSA enrichment
  10. 2026-09-17 19:32 UTCEPSS rescore
  11. 2026-09-17 06:59 UTCGHSA enrichment
  12. 2026-09-16 18:38 UTCEG score recompute
  13. 2026-09-16 18:38 UTCGHSA enrichment
  14. 2026-09-16 14:09 UTCEPSS rescore
  15. 2026-09-16 05:15 UTCEPSS rescore
  16. 2026-09-16 04:30 UTCGHSA enrichment
  17. 2026-09-15 15:44 UTCGHSA enrichment
  18. 2026-09-15 03:22 UTCEG score recompute
  19. 2026-09-15 03:22 UTCGHSA enrichment
  20. 2026-09-15 03:12 UTCEPSS rescore
  21. 2026-09-15 03:12 UTCEPSS rescore
  22. 2026-09-14 15:02 UTCGHSA enrichment
  23. 2026-09-14 02:42 UTCEG score recompute
  24. 2026-09-14 02:42 UTCGHSA enrichment
  25. 2026-09-13 14:21 UTCGHSA enrichment
Show 46 more
  1. 2026-09-13 02:01 UTCEG score recompute
  2. 2026-09-13 02:01 UTCGHSA enrichment
  3. 2026-09-12 13:41 UTCGHSA enrichment
  4. 2026-09-12 01:21 UTCEG score recompute
  5. 2026-09-12 01:21 UTCGHSA enrichment
  6. 2026-09-11 14:53 UTCEPSS rescore
  7. 2026-09-11 14:53 UTCEPSS rescore
  8. 2026-09-11 13:01 UTCEG score recompute
  9. 2026-09-11 13:01 UTCGHSA enrichment
  10. 2026-09-11 00:41 UTCGHSA enrichment
  11. 2026-09-10 12:21 UTCEG score recompute
  12. 2026-09-10 12:21 UTCGHSA enrichment
  13. 2026-09-10 00:01 UTCGHSA enrichment
  14. 2026-09-09 11:41 UTCGHSA enrichment
  15. 2026-09-08 23:21 UTCEG score recompute
  16. 2026-09-08 23:21 UTCGHSA enrichment
  17. 2026-09-08 22:01 UTCEPSS rescore
  18. 2026-09-08 11:00 UTCGHSA enrichment
  19. 2026-09-07 22:17 UTCEG score recompute
  20. 2026-09-07 22:17 UTCGHSA enrichment
  21. 2026-09-07 09:57 UTCGHSA enrichment
  22. 2026-09-06 21:30 UTCEG score recompute
  23. 2026-09-06 21:30 UTCGHSA enrichment
  24. 2026-09-06 13:48 UTCEPSS rescore
  25. 2026-09-06 09:09 UTCGHSA enrichment
  26. 2026-09-05 20:48 UTCEG score recompute
  27. 2026-09-05 20:48 UTCGHSA enrichment
  28. 2026-09-05 15:31 UTCEPSS rescore
  29. 2026-09-05 08:29 UTCGHSA enrichment
  30. 2026-09-04 20:08 UTCEG score recompute
  31. 2026-09-04 20:08 UTCGHSA enrichment
  32. 2026-09-04 07:42 UTCEG score recompute
  33. 2026-09-04 07:42 UTCGHSA enrichment
  34. 2026-09-04 05:07 UTCEPSS rescore
  35. 2026-09-03 19:20 UTCGHSA enrichment
  36. 2026-09-03 18:05 UTCGHSA enrichment
  37. 2026-09-03 07:53 UTCEG score recompute
  38. 2026-09-03 07:53 UTCGHSA enrichment
  39. 2026-09-02 19:32 UTCGHSA enrichment
  40. 2026-09-02 18:57 UTCEG score recompute▲ 7.50
  41. 2026-09-02 18:57 UTCGHSA enrichment
  42. 2026-09-02 18:55 UTCMITRE cvelistV5CVSS v3 → 7.5 · severity → HIGH
  43. 2026-09-02 14:12 UTCEPSS rescore
  44. 2026-09-01 22:18 UTCNVD update
  45. 2026-09-01 21:43 UTCEG score recompute
  46. 2026-09-01 21:42 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-84640?
CVE-2026-84640 is a high vulnerability published on September 1, 2026. A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
When was CVE-2026-84640 disclosed?
CVE-2026-84640 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-2026-84640 actively exploited?
CVE-2026-84640 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 81.6% of all scored CVEs.
What is the CVSS score of CVE-2026-84640?
CVE-2026-84640 has a CVSS v3.1 base score of 7.5 (CISA-ADP / Vulnrichment enrichment; NVD's own analysis pending).
How do I remediate CVE-2026-84640?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-84640, 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

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-84640

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