CVE-2021-3647

Description

### 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](https://url.spec.whatwg.org/), including web browsers and [Node's built-in URL class](https://nodejs.org/api/url.html). ### 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](https://github.com/medialize/URI.js/pull/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](https://github.com/ready-research) via https://huntr.dev/

How to fix CVE-2021-3647

To remediate CVE-2021-3647, upgrade the affected package to a fixed version below.

• —upgrade to 1.19.7 or later

Is CVE-2021-3647 being exploited?

Low — EPSS is 0.2%, meaning exploitation activity has not been observed at scale.

Affected packages (1)