Vulnerability · Published Sep 6, 2026 · Assigned by VulnCheck

CVE-2026-86251h3 before 1.15.9 Path Traversal via Double Decoding

Medium 5.9

In plain English

A medium-severity path traversal in h3 from h3js. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 37% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium

Exploit odds (30 days)0.4%top 62.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	h3	1.15.9	GHSA-72gr-qfp7-vwhw

Affected products (as reported)

Vendor	Product	Versions
h3js	h3	0 – before 1.15.9

Weakness: CWE-22 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

References

GitHub Security Advisory (GHSA-72gr-qfp7-vwhw) vendor-advisory
VulnCheck Advisory: h3 before 1.15.9 Path Traversal via Double Decoding third-party-advisory