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[ CVE-2026-84394 · Published 2 Sep 2026 ]

fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority

CVSS 7.5 EPSS <1%2 agency advisoriesFix available

[ Description ]Official description

fast-uri accepts a host that contains an unbalanced or misplaced authority bracket without reporting an error. A host that starts with an opening bracket but does not end with a closing bracket is neither validated as an IP literal nor canonicalized as a domain name, so parse() returns it as the host with error undefined, while Node's URL and the HTTP clients built on it resolve the same string to a different host. An application that reads the parsed host to make a host decision, such as an SSRF denylist, a redirect allowlist, or proxy routing, and then passes the original URL to an HTTP client evaluates its policy against a string that is not the host the request reaches. The same host is carried through normalize, equal, and resolve. This affects fast-uri versions 2.4.5, 3.1.6, and 4.1.3, and is fixed in 2.4.6, 3.1.7, and 4.1.4, where parse() reports a malformed host for any host that contains a bracket but is not a valid IPv6 literal.

[ Fixes ]Fixes and patches

  • fast-uri 2.4.6Fixed version · GitHub Advisories · npm package fast-uri: upgrade to 2.4.6 or later (affected = 2.4.5)
  • fast-uri 3.1.7Fixed version · GitHub Advisories · npm package fast-uri: upgrade to 3.1.7 or later (affected = 3.1.6)
  • fast-uri 4.1.4Fixed version · GitHub Advisories · npm package fast-uri: upgrade to 4.1.4 or later (affected = 4.1.3)

[ Advisories ]Government CERT advisories

[ Packages ]Affected open-source packages

[ References ]References