GHSA-5jgf-p345-68v8 fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references

• npm fast-uri: >= 2.4.2, < 2.4.5 → fixed in 2.4.5 • npm fast-uri: >= 3.1.3, < 3.1.6 → fixed in 3.1.6 • npm fast-uri: >= 4.0.1, < 4.1.3 → fixed in 4.1.3

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.