An improper input validation flaw was found in urijs where white space characters are not removed from the beginning of an URL. This issue allows bypassing the protocol validation.

A flaw was found in urijs due to the fix of CVE-2021-3647 not considering case-sensitive protocol schemes in the URL. This issue allows attackers to bypass the patch.

Impact If using affected versions to determine a URL's hostname, the hostname can be spoofed by using a combination of backslash (\) and slash (/) characters as part of the scheme delimiter, e.g. scheme:/\/\/\hostname. 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.

Example URL: https:/\/\/\expected-example.com/path Escaped string: https:/\\/\\/\\expected-example.com/path (JavaScript strings must escape backslash)

Affected versions incorrectly return no hostname. 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.

Patches Version 1.19.7 is patched against all known payload variants.

References https://github.com/medialize/URI.js/releases/tag/v1.19.7 (fix for this particular bypass) https://github.com/medialize/URI.js/releases/tag/v1.19.6 (fix for related bypass) https://github.com/medialize/URI.js/releases/tag/v1.19.4 (fix for related bypass) https://github.com/medialize/URI.js/releases/tag/v1.19.3 (fix for related bypass) PR #233 (initial fix for backslash handling)

For more information If you have any questions or comments about this advisory, open an issue in https://github.com/medialize/URI.js

Reporter credit ready-research via https://huntr.dev/