CVE-2026-8950

CRITICALNVD 9.39.3—
EchelonGraph scoreMEDIUM confidence

Score 9.3 from GitHub Security Advisory (severity: CRITICAL) published 2026-05-19. NVD baseline CVSS 9.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
9.3EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.3Exploit: None knownExposed: 0

A fix is available — apply it.

Same-origin policy bypass in the Networking: HTTP component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

CVSS v3
9.3
EG Score
9.3(medium)
EG Risk
42(Track)
EG Risk 42/100SSVC: 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
Severity93% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
9%
KEV
Not listed

Published

May 19, 2026

Last Modified

May 20, 2026

Advisory Details (5)

Auto-updated Sep 15, 2026
🔬 Proof of concept available. 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🟡 PoC Available

1965430 - (CVE-2026-8950) Form POST requests do not set Origin header to null after redirect

https://bugzilla.mozilla.org/show_bug.cgi?id=1965430

Vendor Advisories for CVE-2026-8950(20)

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

Patch Availability(21)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatfirefox-0:140.11.0-1.el10_02026-06-22redhat
redhatfirefox-0:140.11.0-1.el8_62026-06-17redhat
redhatfirefox-0:140.11.0-1.el7_92026-06-17redhat
redhatfirefox-0:140.11.0-1.el8_82026-06-17redhat
redhatthunderbird-0:140.11.0-1.el8_62026-06-17redhat
redhatfirefox-0:140.11.0-1.el8_42026-06-17redhat
redhatthunderbird-0:140.11.0-1.el9_62026-06-17redhat
redhatfirefox-0:140.11.0-1.el9_62026-06-17redhat
redhatfirefox-0:140.11.0-1.el9_22026-06-17redhat
redhatfirefox-0:140.11.0-1.el9_42026-06-17redhat
redhatthunderbird-0:140.11.0-1.el10_02026-06-17redhat
redhatthunderbird-0:140.11.0-1.el9_42026-06-16redhat
redhatthunderbird-0:140.11.0-1.el8_42026-06-16redhat
redhatthunderbird-0:140.11.0-1.el8_82026-06-16redhat
redhatthunderbird-0:140.11.0-1.el9_22026-06-16redhat
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
redhatfirefox-0:140.11.0-1.el9_82026-05-27redhat
redhatfirefox-0:140.11.0-1.el8_102026-05-27redhat
redhatfirefox-0:140.11.0-1.el10_22026-05-27redhat

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.

Affected Packages

(8 across 4 ecosystems)
Debian:11(2)
PackageVulnerable rangeFixed inDependents
firefox-esr102.1.0esr-1 ... 91.9.1esr-1~deb9u1 (275 versions)140.11.0esr-1~deb11u1—
thunderbird1:102.0.1-1 ... 1:91.9.0-1~deb9u1 (326 versions)1:140.11.0esr-1~deb11u1—
Debian:12(2)
PackageVulnerable rangeFixed inDependents
firefox-esr102.11.0esr-1 ... 140.9.1esr-1~deb13u1 (182 versions)140.11.0esr-1~deb12u1—
thunderbird1:102.11.0-1 ... 1:140.9.1esr-1~deb13u1 (211 versions)1:140.11.0esr-1~deb12u1—
Debian:13(2)
PackageVulnerable rangeFixed inDependents
firefox-esr128.13.0esr-1 ... 140.9.1esr-1~deb13u1 (58 versions)140.11.0esr-1~deb13u1—
thunderbird1:128.13.0esr-1 ... 1:140.9.1esr-1~deb13u1 (67 versions)1:140.11.0esr-1~deb13u1—
Debian:14(2)
PackageVulnerable rangeFixed inDependents
firefox-esr128.13.0esr-1 ... 140.9.1esr-1~deb13u1 (59 versions)140.11.0esr-1—
thunderbird1:128.13.0esr-1 ... 1:140.9.1esr-1~deb13u1 (68 versions)1:140.11.0esr-1—

Weakness Classification(1)

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

Additional Vendor Advisories

(1)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 6× in last 7d / 35× 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 471 total refreshes for this CVE.

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

Frequently asked(5)

What is CVE-2026-8950?
CVE-2026-8950 is a critical vulnerability published on May 19, 2026. Same-origin policy bypass in the Networking: HTTP component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.
When was CVE-2026-8950 disclosed?
CVE-2026-8950 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-2026-8950 actively exploited?
CVE-2026-8950 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 90.6% of all scored CVEs.
What is the CVSS score of CVE-2026-8950?
CVE-2026-8950 has a CVSS v3 base score of 9.3 (NVD).
How do I remediate CVE-2026-8950?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-8950, 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-2026-8950

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