CVE-2021-27516

Description

### Impact If using affected versions to determine a URL's hostname, the hostname can be spoofed by using a backslash (`\`) character 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 1.19.6 is patched against all known payload variants. ### References https://github.com/medialize/URI.js/releases/tag/v1.19.6 (fix for this particular 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 [Yaniv Nizry](https://twitter.com/ynizry) from the CxSCA AppSec team at Checkmarx

How to fix CVE-2021-27516

To remediate CVE-2021-27516, upgrade the affected package to a fixed version below.

• —upgrade to 1.19.6 or later

Is CVE-2021-27516 being exploited?

Low — EPSS is 0.6%, meaning exploitation activity has not been observed at scale.

Affected packages (1)

• from 0, < 1.19.6