CVE-2026-86251
Medium
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.
SeverityMedium
CVSS5.9
Exploit probability—
ProductH3
PublishedSep 6, 2026
First seenSep 6, 2026
Weakness typeCWE-22Path traversal
How to fix
Update
- h31.15.9 or later
Vendor advisories
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| h3npm | v < 1.15.9 | 1.15.9 |
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