h3js h3 up to 1.15.8 serveStatic utility resolveDotSegments path traversal

Summaryinfo

A vulnerability classified as problematic was found in h3js h3 up to 1.15.8. Affected is the function resolveDotSegments of the component serveStatic utility. The manipulation results in path traversal. This vulnerability is known as CVE-2026-86251. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability classified as problematic has been found in h3js h3 up to 1.15.8. Affected is the function resolveDotSegments of the component serveStatic utility. The manipulation with an unknown input leads to a path traversal vulnerability. CWE is classifying the issue as CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. This is going to have an impact on confidentiality. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-86251 since 09/06/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1006.

Upgrading to version 1.15.9 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-72107). Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• h3js

Name

• h3

Version

• 1.15.0
• 1.15.1
• 1.15.2
• 1.15.3
• 1.15.4
• 1.15.5
• 1.15.6
• 1.15.7
• 1.15.8

Website

• Product: https://github.com/h3js/h3/

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Once again VulDB remains the best source for vulnerability data.

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