CVE-2026-86251

MEDIUMPre-NVD 5.95.9—
EchelonGraph scoreHIGH confidence

Score 5.9 from GitHub Security Advisory (severity: HIGH) published 2026-09-06. a secondary CVSS source baseline 5.9; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this weekElevated
5.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.9Exploit: Elevated riskExposed: 0

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

h3 versions before 1.15.9 contain a path traversal vulnerability in the serveStatic utility. A double-decoding flaw allows a request path containing double-encoded dot sequences (e.g. %252e%252e) to be decoded to %2e%2e, which survives resolveDotSegments() because that function only checks for literal '.' characters. When the resulting asset ID is resolved by URL-based backends (CDN, S3, object storage), %2e%2e is interpreted as '..' per RFC 3986, enabling path traversal to read arbitrary files from the backend.

CVSS v3
5.9
EG Score
5.9(high)
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
Severity59% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
23%
KEV
Not listed

Published

September 6, 2026

Last Modified

September 9, 2026

Advisory Details (2)

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

h3 before 1.15.9 Path Traversal via Double Decoding | Advisories | VulnCheck

https://www.vulncheck.com/advisories/h3-before-1.15.9-path-traversal-via-double-decoding
github Patch Available🟡 PoC Available

Double Decoding in `serveStatic` Bypasses `resolveDotSegments` Path Traversal Protection via `%252e%252e` · Advisory · h3js/h3 · GitHub

https://github.com/h3js/h3/security/advisories/GHSA-72gr-qfp7-vwhw

Vendor Advisories for CVE-2026-86251(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
h3—1.15.9—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 19× in last 7d / 38× 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 04:03 UTCEG score recompute
  2. 2026-09-19 04:03 UTCGHSA enrichment
  3. 2026-09-18 19:28 UTCEPSS rescore
  4. 2026-09-18 02:35 UTCEG score recompute
  5. 2026-09-18 02:35 UTCGHSA enrichment
  6. 2026-09-17 19:32 UTCEPSS rescore
  7. 2026-09-17 01:06 UTCEG score recompute
  8. 2026-09-17 01:06 UTCGHSA enrichment
  9. 2026-09-16 14:09 UTCEPSS rescore
  10. 2026-09-16 05:15 UTCEPSS rescore
  11. 2026-09-15 23:37 UTCEG score recompute
  12. 2026-09-15 23:37 UTCGHSA enrichment
  13. 2026-09-15 03:12 UTCEPSS rescore
  14. 2026-09-15 03:12 UTCEPSS rescore
  15. 2026-09-14 22:08 UTCGHSA enrichment
  16. 2026-09-13 20:39 UTCEG score recompute
  17. 2026-09-13 20:39 UTCGHSA enrichment
  18. 2026-09-12 19:11 UTCEG score recompute
  19. 2026-09-12 19:11 UTCGHSA enrichment
  20. 2026-09-11 17:43 UTCEG score recompute
  21. 2026-09-11 17:43 UTCGHSA enrichment
  22. 2026-09-11 14:53 UTCEPSS rescore
  23. 2026-09-11 14:53 UTCEPSS rescore
  24. 2026-09-10 16:14 UTCEG score recompute
  25. 2026-09-10 16:14 UTCGHSA enrichment
Show 13 more
  1. 2026-09-09 14:31 UTCEG score recompute
  2. 2026-09-09 14:31 UTCGHSA enrichment
  3. 2026-09-09 14:09 UTCEG score recompute
  4. 2026-09-09 14:09 UTCGHSA enrichment
  5. 2026-09-08 22:01 UTCEPSS rescore
  6. 2026-09-08 20:13 UTCGHSA enrichment
  7. 2026-09-08 16:16 UTCEG score recompute
  8. 2026-09-08 16:15 UTCGHSA enrichment
  9. 2026-09-07 14:07 UTCEG score recompute
  10. 2026-09-07 14:07 UTCGHSA enrichment
  11. 2026-09-06 12:22 UTCEG score recompute
  12. 2026-09-06 12:13 UTCEG score recompute
  13. 2026-09-06 12:09 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-86251?
CVE-2026-86251 is a medium vulnerability published on September 6, 2026. h3 versions before 1.15.9 contain a path traversal vulnerability in the serveStatic utility. A double-decoding flaw allows a request path containing double-encoded dot sequences (e.g. %252e%252e) to be decoded to %2e%2e, which survives resolveDotSegments() because that function only checks for…
When was CVE-2026-86251 disclosed?
CVE-2026-86251 was first published in the National Vulnerability Database on September 6, 2026, with the most recent update on September 9, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-86251 actively exploited?
CVE-2026-86251 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 77.4% of all scored CVEs.
What is the CVSS score of CVE-2026-86251?
CVE-2026-86251 has a CVSS v3 base score of 5.9 (NVD).
How do I remediate CVE-2026-86251?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-86251, 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-2026-86251

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