CVE-2026-8959

CRITICALNVD 9.69.6—
EchelonGraph scoreMEDIUM confidence

Score 9.6 from GitHub Security Advisory (severity: CRITICAL) published 2026-05-19. NVD baseline CVSS 9.6; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Trending — 4 sources updated this week
9.6EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.6Exploit: None knownExposed: 0

A fix is available — apply it.

Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

CVSS v3
9.6
EG Score
9.6(medium)
EG Risk
43(Track)
EG Risk 43/100SSVC: 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
Severity96% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
34%
KEV
Not listed

Published

May 19, 2026

Last Modified

May 20, 2026

Advisory Details (5)

Auto-updated Aug 23, 2026
No patch confirmed yet.
generic

Security Vulnerabilities fixed in Thunderbird 140.11 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-51/
generic

Security Vulnerabilities fixed in Thunderbird 151 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-50/
generic

Security Vulnerabilities fixed in Firefox ESR 140.11 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-48/
generic

Security Vulnerabilities fixed in Firefox 151 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-46/
generic

Access Denied

https://bugzilla.mozilla.org/show_bug.cgi?id=2034754

Vendor Advisories for CVE-2026-8959(11)

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

Patch Availability(10)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatthunderbird-0:140.11.0-1.el10_02026-06-17redhat
redhatthunderbird-0:140.11.0-1.el9_62026-06-17redhat
redhatthunderbird-0:140.11.0-1.el8_62026-06-17redhat
redhatthunderbird-0:140.11.0-1.el8_82026-06-16redhat
redhatthunderbird-0:140.11.0-1.el8_42026-06-16redhat
redhatthunderbird-0:140.11.0-1.el9_22026-06-16redhat
redhatthunderbird-0:140.11.0-1.el9_42026-06-16redhat
redhatthunderbird-0:140.11.0-1.el8_102026-06-03redhat
redhatthunderbird-0:140.11.0-1.el10_22026-06-01redhat
redhatthunderbird-0:140.11.0-1.el9_82026-05-27redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(3)

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

Data Freshness Timeline

(refreshed 17× in last 7d / 178× 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 451 total refreshes for this CVE.

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

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Frequently asked(5)

What is CVE-2026-8959?
CVE-2026-8959 is a critical vulnerability published on May 19, 2026. Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.
When was CVE-2026-8959 disclosed?
CVE-2026-8959 was first published in the National Vulnerability Database on May 19, 2026, with the most recent update on May 20, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-8959 actively exploited?
CVE-2026-8959 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 65.5% of all scored CVEs.
What is the CVSS score of CVE-2026-8959?
CVE-2026-8959 has a CVSS v3 base score of 9.6 (NVD).
How do I remediate CVE-2026-8959?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-8959, 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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