Hostname spoofing via backslashes in URL

Overview

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.

Recommendation

Upgrade to version 1.19.7 or later

References

• GitHub Advisory
• CVE
• 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)