GHSA-5jgf-p345-68v8

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GHSA-5jgf-p345-68v8

Summary: fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references

Details: ### 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.

References: 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, 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