fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references
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 software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | fast-uri | >= 2.4.2, < 2.4.5, >= 3.1.3, < 3.1.6, >= 4.0.1, < 4.1.3 | 2.4.5, 3.1.6, 4.1.3 |
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
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N- Weakness (CWE)
CWE-436- Platform
- npm
- Package
fast-uri- Disclosed
- 02.09.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-5jgf-p345-68v8 - CC BY 4.0
Vulnerability history: fast-uri
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 13
- First → latest
- 05.2026 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 11
- Medium 2
Disclosures per year
- 2026: 13
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