CVE-2026-86251
h3 before 1.15.9 Path Traversal via Double Decoding
- State
- Published
- Severity
- 8.2 High
- Published
- Sep 6, 2026
- Updated
- Sep 9, 2026
- Reserved
- Sep 6, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 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 | VulnCheck |
| 3.1 | 5.9 Medium | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N | VulnCheck |
Weaknesses
- CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Affected Products
| Product | Versions |
|---|---|
h3h3js |
|
References
- GitHub Security Advisory (GHSA-72gr-qfp7-vwhw)vendor-advisory
- VulnCheck Advisory: h3 before 1.15.9 Path Traversal via Double Decodingthird-party-advisory
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