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.

Affected: npm: fast-uri

### Impact

`fast-uri` accepts a host that contains an unbalanced or misplaced authority bracket (`[` or `]`) without reporting an error. A host that starts with `[` but does not end with `]`, such as `[@127.0.0.1`, 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 `http.get`, `axios`, `got`, and other clients built on it) resolve the same string to `127.0.0.1`. An application that reads `parse().host` to make a host decision (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()`.

### Patches

This vulnerability has been patched in fast-uri `4.1.4`, `3.1.7`, and `2.4.6`. `parse()` now reports `URI host is malformed.` for any host that contains a bracket but is not a valid `[IPv6]` literal. All users should upgrade.

### Workarounds

If upgrading is not immediately possible, reject any URL whose host contains a `[` or `]` that is not a well-formed IPv6 literal before making a host decision. Clients that fail closed on credential-bearing URLs, such as Node's global `fetch()`, are not affected by the reported vector.

fast-uri: fast-uri: Authority Injection via Unvalidated Port Serialization fast-uri: fast-uri: Host confusion via unbalanced URI brackets can bypass security policies undici: undici: Denial of Service via unhandled error in WebSocket permessage-deflate decompression undici: undici: Authentication bypass via cross-origin cache poisoning due to missing origin isolation

Affected: Ubuntu:18.04:LTS: node-ajv, Ubuntu:20.04:LTS: node-ajv, Ubuntu:22.04:LTS: node-ajv, Ubuntu:24.04:LTS: node-ajv, Ubuntu:26.04:LTS: node-ajv

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.

Ein Angreifer kann mehrere Schwachstellen in Red Hat Ansible Automation Platform ausnutzen, um seine Privilegien zu erhöhen, beliebigen Code auszuführen, Sicherheitsmaßnahmen zu umgehen, Daten zu manipulieren oder offenzulegen und einen Denial-of-Service-Zustand herbeizuführen.