CVE-2021-37699

Next.js is an open source website development framework to be used with the React library. In affected versions specially encoded paths could be used when pages/_error.js was statically generated, allowing an open redirect to occur to an external site. In general, this redirect does not directly harm users although it can allow for phishing attacks by redirecting to an attacker's domain from a trusted domain.

• Affected: Users of Next.js between 10.0.5 and 10.2.0
• Affected: Users of Next.js between 11.0.0 and 11.0.1 using pages/_error.js without getInitialProps
• Affected: Users of Next.js between 11.0.0 and 11.0.1 using pages/_error.js and next export
• Not affected: Deployments on Vercel (vercel.com) are not affected
• Not affected: Deployments with pages/404.js
• Note that versions prior to 0.9.9 package next npm package hosted a different utility (0.4.1 being the latest version of that codebase), and this advisory does not apply to those versions.

We recommend upgrading to the latest version of Next.js to improve the overall security of your application.

Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.

CVE-2021-37699 has a CVSS score of 6.9 (Medium). The vector is network-reachable, no privileges required, and user interaction required. 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 (11.1.0); upgrading removes the vulnerable code path.

Kodem intelligence

https://github.com/vercel/next.js/releases/tag/v11.1.0

1. What is CVE-2021-37699? CVE-2021-37699 is a medium-severity open redirect vulnerability in next (npm), affecting versions >= 0.9.9, < 11.1.0. It is fixed in 11.1.0. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
2. How severe is CVE-2021-37699? CVE-2021-37699 has a CVSS score of 6.9 (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.
3. Which versions of next are affected by CVE-2021-37699? next (npm) versions >= 0.9.9, < 11.1.0 is affected.
4. Is there a fix for CVE-2021-37699? Yes. CVE-2021-37699 is fixed in 11.1.0. Upgrade to this version or later.
5. Is CVE-2021-37699 exploitable, and should I be worried? Whether CVE-2021-37699 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
6. What actually determines whether CVE-2021-37699 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.
7. How do I fix CVE-2021-37699? Upgrade next to 11.1.0 or later.