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.
Version 1.19.7 is patched against all known payload variants.
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)
If you have any questions or comments about this advisory, open an issue in https://github.com/medialize/URI.js
github.com/medialize/URI.js/commit/ac43ca8f80c042f0256fb551ea5203863dec4481
github.com/medialize/URI.js/pull/233
github.com/medialize/URI.js/releases/tag/v1.19.3
github.com/medialize/URI.js/releases/tag/v1.19.4
github.com/medialize/URI.js/releases/tag/v1.19.6
github.com/medialize/URI.js/releases/tag/v1.19.7
github.com/medialize/URI.js/security/advisories/GHSA-89gv-h8wf-cg8r
huntr.dev/bounties/1625558772840-medialize/URI.js
nvd.nist.gov/vuln/detail/CVE-2021-3647