CVE-2026-84292

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

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').

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.

CVE-2026-84292 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.4.6, 3.1.7, 4.1.4); upgrading removes the vulnerable code path.

Kodem intelligence

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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.

1. What is CVE-2026-84292? CVE-2026-84292 is a high-severity security vulnerability in fast-uri (npm), affecting versions < 2.4.6. It is fixed in 2.4.6, 3.1.7, 4.1.4.
2. How severe is CVE-2026-84292? CVE-2026-84292 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of fast-uri are affected by CVE-2026-84292? fast-uri (npm) versions < 2.4.6 is affected.
4. Is there a fix for CVE-2026-84292? Yes. CVE-2026-84292 is fixed in 2.4.6, 3.1.7, 4.1.4. Upgrade to this version or later.
5. Is CVE-2026-84292 exploitable, and should I be worried? Whether CVE-2026-84292 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-84292 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-84292?
   • Upgrade fast-uri to 2.4.6 or later
   • Upgrade fast-uri to 3.1.7 or later
   • Upgrade fast-uri to 4.1.4 or later

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