fast-uri vulnerable to authority injection via an unvalidated port in serialize

Why it is Yellow

• CVSS 7.5 high
• Remotely exploitable without logging in
• On your watchlist: npm

Affected packages

References

• https://github.com/advisories/GHSA-qw65-cvwx-89v3
• https://github.com/fastify/fast-uri/security/advisories/GHSA-qw65-cvwx-89v3
• https://nvd.nist.gov/vuln/detail/CVE-2026-84292
• https://github.com/fastify/fast-uri/commit/820e8478dd7da3d09f187bfaf35d50b71f67b8b4
• https://cna.openjsf.org/security-advisories.html
• https://github.com/fastify/fast-uri/releases/tag/v2.4.6
• https://github.com/fastify/fast-uri/releases/tag/v3.1.7
• https://github.com/fastify/fast-uri/releases/tag/v4.1.4
• https://github.com/advisories/GHSA-qw65-cvwx-89v3

Original description

### Impact `fast-uri` serializes the `port` component of a URI without validating it. When recomposing the authority, `fast-uri` escapes the userinfo and host components but concatenates the port verbatim, so a `port` value that is not a sequence of digits can inject authority delimiters. For example, serializing a component whose `port` is `@127.0.0.1:8124` produces `http://trusted.example:@127.0.0.1:8124/app`, demoting the intended host to userinfo and pointing the authority at an attacker-controlled host. Both `fast-uri` and Node's `URL` read the result back as the attacker's host with no error, so re-validating the built URI does not catch it. This affects applications that build URIs from parts and assign untrusted data to the `port` component (for example a fixed host from configuration and a port taken from user input or a service record). The same path is reachable through `serialize()`, `normalize()`, and `equal()` in their object forms. A `port` obtained from `parse()` is always digits and is not affected. ### Patches This vulnerability has been patched in fast-uri `4.1.4`, `3.1.7`, and `2.4.6`. `recomposeAuthority` now rejects any port that is not `*DIGIT` per RFC 3986. All users should upgrade. ### Workarounds If upgrading is not immediately possible, validate the `port` value against the RFC 3986 grammar (digits only) before passing a component to `serialize()`, `normalize()`, or `equal()`, and reject anything else, for example `if (!/^\d*$/.test(String(port))) throw new Error('invalid port')`.