CVE-2026-74956

CRITICALPre-NVD 9.19.1—
EchelonGraph scoreHIGH confidence

Score 9.1 from GitHub Security Advisory (severity: CRITICAL) published 2026-08-18. 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 — 5 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.

Same-origin policy bypass in the DOM: Service Workers component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

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
21%
KEV
Not listed

Published

August 18, 2026

Last Modified

August 19, 2026

Advisory Details (5)

Auto-updated Aug 18, 2026
No patch confirmed yet.
generic

Security Vulnerabilities fixed in Thunderbird 153.1 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-80/
generic

Security Vulnerabilities fixed in Thunderbird 154 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-78/
generic

Security Vulnerabilities fixed in Firefox ESR 153.1 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-77/
generic

Security Vulnerabilities fixed in Firefox 154 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-74/
generic

Access Denied

https://bugzilla.mozilla.org/show_bug.cgi?id=2032406

Vendor Advisories for CVE-2026-74956(1)

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

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 30× in last 7d / 30× 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. 2026-08-21 04:44 UTCGHSA enrichment
  2. 2026-08-21 00:26 UTCEG score recompute
  3. 2026-08-21 00:26 UTCGHSA enrichment
  4. 2026-08-20 22:56 UTCEPSS rescore
  5. 2026-08-20 20:09 UTCGHSA enrichment
  6. 2026-08-20 15:51 UTCGHSA enrichment
  7. 2026-08-20 11:34 UTCGHSA enrichment
  8. 2026-08-20 07:14 UTCGHSA enrichment
  9. 2026-08-20 02:56 UTCGHSA enrichment
  10. 2026-08-19 22:38 UTCGHSA enrichment
  11. 2026-08-19 18:20 UTCEG score recompute
  12. 2026-08-19 18:20 UTCGHSA enrichment
  13. 2026-08-19 17:04 UTCEPSS rescore
  14. 2026-08-19 14:02 UTCGHSA enrichment
  15. 2026-08-19 09:44 UTCGHSA enrichment
  16. 2026-08-19 05:26 UTCGHSA enrichment
  17. 2026-08-19 01:08 UTCGHSA enrichment
  18. 2026-08-19 00:42 UTCEG score recompute
  19. 2026-08-19 00:42 UTCGHSA enrichment
  20. 2026-08-18 20:24 UTCGHSA enrichment
  21. 2026-08-18 20:21 UTCNVD updateCVSS v3 → 9.1 · severity → CRITICAL
  22. 2026-08-18 19:23 UTCNVD update
  23. 2026-08-18 19:19 UTCEG score recompute▲ 9.10
  24. 2026-08-18 19:19 UTCGHSA enrichment
  25. 2026-08-18 19:18 UTCMITRE cvelistV5CVSS v3 → 9.1 · severity → CRITICAL
Show 5 more
  1. 2026-08-18 19:05 UTCGHSA enrichment
  2. 2026-08-18 19:04 UTCMITRE cvelistV5
  3. 2026-08-18 13:19 UTCNVD update
  4. 2026-08-18 12:42 UTCEG score recompute
  5. 2026-08-18 12:41 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-74956?
CVE-2026-74956 is a critical vulnerability published on August 18, 2026. Same-origin policy bypass in the DOM: Service Workers component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.
When was CVE-2026-74956 disclosed?
CVE-2026-74956 was first published in the National Vulnerability Database on August 18, 2026, with the most recent update on August 19, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-74956 actively exploited?
CVE-2026-74956 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 79.2% of all scored CVEs.
What is the CVSS score of CVE-2026-74956?
CVE-2026-74956 has a CVSS v3.1 base score of 9.1 (CISA-ADP / Vulnrichment enrichment; NVD's own analysis pending).
How do I remediate CVE-2026-74956?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-74956, 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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