Vulnerability-Lookup

CVE-2026-86251 (GCVE-0-2026-86251)

Vulnerability from cvelistv5 – Published: 2026-09-06 12:00 – Updated: 2026-09-09 13:57

Title

h3 before 1.15.9 Path Traversal via Double Decoding

Summary

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.

Severity

8.2 (High)


                        
                          CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

5.9 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-09 13:57 UTC

CWE

CWE-22 - Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Assigner

VulnCheck mitre root

References

2 references

URL	Tags
https://github.com/h3js/h3/security/advisories/GH…	vendor-advisory
https://www.vulncheck.com/advisories/h3-before-1.…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version	CPE status
h3js	h3	Affected: 0 , < 1.15.9 (semver) Unaffected: 1.15.9 (semver)	guessed

Date Public

2026-03-20 00:00

Credits

offset

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-86251

Vulnerability from fkie_nvd - Published: 2026-09-06 12:17 - Updated: 2026-09-09 14:17

Severity

5.9 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Summary

References

	URL	Tags
	disclosure@vulncheck.com	https://github.com/h3js/h3/security/advisories/GHSA-72gr-qfp7-vwhw
	disclosure@vulncheck.com	https://www.vulncheck.com/advisories/h3-before-1.15.9-path-traversal-via-double-decoding
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/h3js/h3/security/advisories/GHSA-72gr-qfp7-vwhw

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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GHSA-676V-2C25-VQPJ

Vulnerability from github – Published: 2026-09-06 12:30 – Updated: 2026-09-06 12:30

Details

Severity

5.9 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

8.2 (High)


                  
                    CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Show details on source website

JSON

To clipboard

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  "affected": [],
  "aliases": [
    "CVE-2026-86251"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-22"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-06T12:17:15Z",
    "severity": "HIGH"
  },
  "details": "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 \u0027.\u0027 characters. When the resulting asset ID is resolved by URL-based backends (CDN, S3, object storage), %2e%2e is interpreted as \u0027..\u0027 per RFC 3986, enabling path traversal to read arbitrary files from the backend.",
  "id": "GHSA-676v-2c25-vqpj",
  "modified": "2026-09-06T12:30:23Z",
  "published": "2026-09-06T12:30:23Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/h3js/h3/security/advisories/GHSA-72gr-qfp7-vwhw"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-86251"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/h3-before-1.15.9-path-traversal-via-double-decoding"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

CVE-2026-86251 (GCVE-0-2026-86251)

FKIE_CVE-2026-86251

GHSA-676V-2C25-VQPJ

Tags

Sightings

Nomenclature