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CVE-2026-84394
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.
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The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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