CVE-2026-86205

MEDIUMPre-NVD 5.45.4—
EchelonGraph scoreHIGH confidence

Score 5.4 from GitHub Security Advisory published 2026-09-06. a secondary CVSS source baseline 5.4; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this weekElevated
5.4EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.4Exploit: Elevated riskExposed: 0

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

h3 versions before 2.0.1-rc.18 contain an open redirect vulnerability in the redirectBack() utility that fails to sanitize protocol-relative paths in the Referer header pathname. Attackers can craft a same-origin URL with a double-slash path segment that passes origin validation but produces a Location header interpreted by browsers as a protocol-relative redirect to an external domain.

CVSS v3
5.4
EG Score
5.4(high)
EG Risk
40(Track)
EG Risk 40/100SSVC: 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
Severity54% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
10%
KEV
Not listed

Published

September 6, 2026

Last Modified

September 8, 2026

Advisory Details (2)

Auto-updated Sep 6, 2026
🔬 Proof of concept available. Patch available. Sources: github.
generic

h3 before 2.0.1-rc.18 Open Redirect via redirectBack() | Advisories | VulnCheck

https://www.vulncheck.com/advisories/h3-before-2.0.1-rc.18-open-redirect-via-redirectback
github Patch Available🟡 PoC Available

Open Redirect via Protocol-Relative Path in `redirectBack()` Referer Validation · Advisory · h3js/h3 · GitHub

https://github.com/h3js/h3/security/advisories/GHSA-fp4x-ggrf-wmc6

Vendor Advisories for CVE-2026-86205(1)

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

Affected Packages

(1 across 1 ecosystem)
npm(1)
PackageVulnerable rangeFixed inDependents
h32.0.1-rc.172.0.1-rc.18—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 20× in last 7d / 39× 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 08:53 UTCEG score recompute
  2. 2026-09-19 08:53 UTCGHSA enrichment
  3. 2026-09-18 19:28 UTCEPSS rescore
  4. 2026-09-18 07:48 UTCEG score recompute
  5. 2026-09-18 07:48 UTCGHSA enrichment
  6. 2026-09-17 19:32 UTCEPSS rescore
  7. 2026-09-17 06:45 UTCEG score recompute
  8. 2026-09-17 06:45 UTCGHSA enrichment
  9. 2026-09-16 14:09 UTCEPSS rescore
  10. 2026-09-16 05:32 UTCEG score recompute
  11. 2026-09-16 05:32 UTCGHSA enrichment
  12. 2026-09-16 05:15 UTCEPSS rescore
  13. 2026-09-15 04:30 UTCEG score recompute
  14. 2026-09-15 04:30 UTCGHSA enrichment
  15. 2026-09-15 03:12 UTCEPSS rescore
  16. 2026-09-15 03:12 UTCEPSS rescore
  17. 2026-09-14 03:27 UTCEG score recompute
  18. 2026-09-14 03:27 UTCGHSA enrichment
  19. 2026-09-13 02:25 UTCEG score recompute
  20. 2026-09-13 02:25 UTCGHSA enrichment
  21. 2026-09-12 01:23 UTCEG score recompute
  22. 2026-09-12 01:23 UTCGHSA enrichment
  23. 2026-09-11 14:53 UTCEPSS rescore
  24. 2026-09-11 14:53 UTCEPSS rescore
  25. 2026-09-11 00:21 UTCEG score recompute
Show 14 more
  1. 2026-09-11 00:21 UTCGHSA enrichment
  2. 2026-09-09 23:19 UTCEG score recompute
  3. 2026-09-09 23:19 UTCGHSA enrichment
  4. 2026-09-08 22:01 UTCEPSS rescore
  5. 2026-09-08 20:13 UTCGHSA enrichment
  6. 2026-09-08 15:11 UTCEG score recompute
  7. 2026-09-08 15:11 UTCGHSA enrichment
  8. 2026-09-08 14:12 UTCEG score recompute
  9. 2026-09-08 14:12 UTCGHSA enrichment
  10. 2026-09-07 14:07 UTCEG score recompute
  11. 2026-09-07 14:07 UTCGHSA enrichment
  12. 2026-09-06 12:22 UTCEG score recompute
  13. 2026-09-06 12:13 UTCEG score recompute
  14. 2026-09-06 12:09 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-86205?
CVE-2026-86205 is a medium vulnerability published on September 6, 2026. h3 versions before 2.0.1-rc.18 contain an open redirect vulnerability in the redirectBack() utility that fails to sanitize protocol-relative paths in the Referer header pathname. Attackers can craft a same-origin URL with a double-slash path segment that passes origin validation but produces a…
When was CVE-2026-86205 disclosed?
CVE-2026-86205 was first published in the National Vulnerability Database on September 6, 2026, with the most recent update on September 8, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-86205 actively exploited?
CVE-2026-86205 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 90.2% of all scored CVEs.
What is the CVSS score of CVE-2026-86205?
CVE-2026-86205 has a CVSS v3 base score of 5.4 (NVD).
How do I remediate CVE-2026-86205?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-86205, 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-2026-86205

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