Summary
Hostname spoofing via backslashes in URL
References
https://github.com/medialize/URI.js/releases/tag/v1.19.4 (complete fix for this bypass)
https://github.com/medialize/URI.js/releases/tag/v1.19.3 (partial fix for this bypass)
PR #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
Impact
If using affected versions to determine a URL's hostname, the hostname can be spoofed by using a backslash (\) character followed by an at (@) character. 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\@observed-example.com
Escaped string: https://expected-example.com\\@observed-example.com (JavaScript strings must escape backslash)
Affected versions incorrectly return observed-example.com. 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.
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
CVE-2020-26291 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.19.4); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Version 1.19.4 is patched against all known payload variants. Version 1.19.3 has a partial patch but is still vulnerable to a payload variant.
Frequently Asked Questions
- What is CVE-2020-26291? CVE-2020-26291 is a medium-severity improper input validation vulnerability in urijs (npm), affecting versions < 1.19.4. It is fixed in 1.19.4. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- How severe is CVE-2020-26291? CVE-2020-26291 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of urijs are affected by CVE-2020-26291? urijs (npm) versions < 1.19.4 is affected.
- Is there a fix for CVE-2020-26291? Yes. CVE-2020-26291 is fixed in 1.19.4. Upgrade to this version or later.
- Is CVE-2020-26291 exploitable, and should I be worried? Whether CVE-2020-26291 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2020-26291 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2020-26291? Upgrade
urijsto 1.19.4 or later.