URI.js is a javascript URL mutation library (npm package urijs). In URI.js before version 1.19.4, the hostname can be spoofed by using a backslash ("\") character followed by an at ("@") character. If the hostname is used in security decisions, the decision may be incorrect. Depending on library usage and attacker intent, impacts may include allow/block list bypasses, SSRF attacks, open redirects, or other undesired behavior. For example the URL "https://expected-example.com\@observed-example.com" will incorrectly return "observed-example.com" if using an affected version. Patched versions correctly return "expected-example.com". Patched versions match the behavior of other parsers which implement the WHATWG URL specification, including web browsers and Node's built-in URL class. Version 1.19.4 is patched against all known payload variants. Version 1.19.3 has a partial patch but is still vulnerable to a payload variant.]