fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references
🔗 CVE IDs covered (1)
📋 Description
Impact
fast-uri canonicalizes a host to its ASCII form only when the input carries an explicit scheme. When resolve() resolves a scheme-relative reference (//host/) against a scheme-bearing base, it still emits the host verbatim even though the effective scheme is known, so re-parsing the resolved URI yields a different host than the one resolve() returned. An application that resolves an untrusted reference with fast-uri and then checks or routes on the resulting host can make a policy decision on one host and reach another. This is an incomplete-fix variant of CVE-2026-13676, whose IDN canonicalization was applied only to the scheme-bearing form.
Patches
Upgrade to fast-uri 2.4.5, 3.1.6, or 4.1.3. resolve() now canonicalizes the host once the effective scheme is known, and fails closed if a raw non-ASCII host cannot be converted.
Workarounds
Resolve scheme-relative references against a base that carries a scheme before performing any host-policy or origin check.
🎯 Affected products3
- npm/fast-uri:>= 2.4.2, < 2.4.5
- npm/fast-uri:>= 3.1.3, < 3.1.6
- npm/fast-uri:>= 4.0.1, < 4.1.3
🔗 References (10)
- https://github.com/fastify/fast-uri/security/advisories/GHSA-5jgf-p345-68v8
- https://nvd.nist.gov/vuln/detail/CVE-2026-75931
- https://github.com/fastify/fast-uri/commit/0256bc8d1f28b5d0ac657faf67e2411a189dfcb5
- https://github.com/fastify/fast-uri/commit/444ecdad447db2cc23c4d422acc6f0daa6fa8eef
- https://github.com/fastify/fast-uri/commit/4e4ebd8b245f6ca16e448203559eea3e545453a3
- https://cna.openjsf.org/security-advisories.html
- https://github.com/fastify/fast-uri/releases/tag/v2.4.5
- https://github.com/fastify/fast-uri/releases/tag/v3.1.6
- https://github.com/fastify/fast-uri/releases/tag/v4.1.3
- https://github.com/advisories/GHSA-5jgf-p345-68v8