CVE-2022-21721

Workarounds

We recommend upgrading whether you can reproduce or not although you can ensure /${locale}/_next/ is blocked from reaching the Next.js instance until you upgrade.

For more information

If you have any questions or comments about this advisory:

• Open an issue in next
• Email us at [email protected]

Vulnerable code could allow a bad actor to trigger a denial of service attack for anyone running a Next.js app at version >= 12.0.0, and using i18n functionality.

• Affected: All of the following must be true to be affected by this CVE
  • Next.js versions above v12.0.0
  • Using next start or a custom server
  • Using the built-in i18n support
• Not affected:
  • Deployments on Vercel (vercel.com) are not affected along with similar environments where invalid requests are filtered before reaching Next.js.

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-2022-21721 has a CVSS score of 5.9 (Medium). The vector is network-reachable, no 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 (12.0.9); upgrading removes the vulnerable code path.

Kodem intelligence

A patch has been released, [email protected], that mitigates this issue. We recommend all affected users upgrade as soon as possible.

1. What is CVE-2022-21721? CVE-2022-21721 is a medium-severity improper input validation vulnerability in next (npm), affecting versions >= 12.0.0, < 12.0.9. It is fixed in 12.0.9. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
2. How severe is CVE-2022-21721? CVE-2022-21721 has a CVSS score of 5.9 (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-2022-21721? next (npm) versions >= 12.0.0, < 12.0.9 is affected.
4. Is there a fix for CVE-2022-21721? Yes. CVE-2022-21721 is fixed in 12.0.9. Upgrade to this version or later.
5. Is CVE-2022-21721 exploitable, and should I be worried? Whether CVE-2022-21721 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-2022-21721 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-2022-21721? Upgrade next to 12.0.9 or later.