Executive brief
fast-uri is a JavaScript library for parsing, normalizing, and serializing URIs. An attacker can inject malicious authority components (hostname redirects) by passing an unvalidated port value containing special characters to the serialize, normalize, or equal functions. This allows an attacker to redirect traffic intended for a legitimate host to an attacker-controlled server without the application detecting the change.
Technical details
The vulnerability is an improper encoding/escaping issue (CWE-116) in fast-uri's recomposeAuthority function. When serializing a URI, the library properly escapes userinfo and host components but concatenates the port value verbatim without validating that it contains only digits per RFC 3986. An attacker can inject authority delimiters (such as @) in the port parameter, which reorders the URI structure—demoting the intended host to the userinfo section and inserting an attacker-controlled host as the actual authority. The attack is network-reachable with no authentication or user interaction required and affects applications that construct URIs from untrusted port values via serialize(), normalize(), or equal() methods. Patches are available in fast-uri 2.4.6, 3.1.7, and 4.1.4, which now validate that the port is a digit sequence.
Affected products
- OpenJS Foundation fast-uri before 2.4.6, 3.0.0 before 3.1.7, 4.0.0 before 4.1.4
Timeline
- 2026-09-02: disclosed: CVE-2026-84292 published
- 2026-09-02: patched: Patches released in versions 2.4.6, 3.1.7, and 4.1.4