high
7.5
CWE
20 918
Advisory Published
Advisory Published
Updated

CVE-2021-27516: Input Validation

First published: Sun Feb 21 2021(Updated: )

### 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

Credit: cve@mitre.org cve@mitre.org

Affected SoftwareAffected VersionHow to fix
Uri.js Project Uri.js<1.19.6
npm/urijs<1.19.6
1.19.6

Remedy

https://github.com/medialize/URI.js/commit/a1ad8bcbc39a4d136d7e252e76e957f3ece70839

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Reference Links

Parent vulnerabilities

(Appears in the following advisories)

Frequently Asked Questions

  • What is CVE-2021-27516?

    CVE-2021-27516 is a vulnerability in URI.js library versions before 1.19.6 that mishandles the use of a backslash character in the scheme delimiter, leading to potential hostname spoofing.

  • How does CVE-2021-27516 impact URL hostname determination?

    If affected versions of URI.js are used to determine a URL's hostname, an attacker can spoof the hostname by using a backslash character as part of the scheme delimiter.

  • What could be the consequences of CVE-2021-27516?

    Depending on how the library is used, if the hostname is used in security decisions, those decisions may be incorrect due to potential spoofing.

  • How can I fix CVE-2021-27516?

    To fix CVE-2021-27516, update to URI.js version 1.19.6 or later.

  • What is the severity of CVE-2021-27516?

    CVE-2021-27516 has a severity keyword of 'high' and a severity value of 7.5 (out of 10).

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