CVE-2026-75931: fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references
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.
References
- cna.openjsf.org/security-advisories.html
- github.com/advisories/GHSA-5jgf-p345-68v8
- github.com/fastify/fast-uri/commit/0256bc8d1f28b5d0ac657faf67e2411a189dfcb5
- github.com/fastify/fast-uri/commit/444ecdad447db2cc23c4d422acc6f0daa6fa8eef
- github.com/fastify/fast-uri/commit/4e4ebd8b245f6ca16e448203559eea3e545453a3
- github.com/fastify/fast-uri/releases/tag/v2.4.5
- github.com/fastify/fast-uri/releases/tag/v3.1.6
- github.com/fastify/fast-uri/releases/tag/v4.1.3
- github.com/fastify/fast-uri/security/advisories/GHSA-5jgf-p345-68v8
- nvd.nist.gov/vuln/detail/CVE-2026-75931
Code Behaviors & Features
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