CVE-2022-21721: Vercel Next.js

High severity, CVSS 7.5. EPSS: 2.2% chance of exploitation in the next 30 days.

Next.js is a React framework. Starting with version 12.0.0 and prior to version 12.0.9, vulnerable code could allow a bad actor to trigger a denial of service attack for anyone using i18n functionality. In order to be affected by this CVE, one must use next start or a custom server and the built-in i18n support. Deployments on Vercel, along with similar environments where invalid requests are filtered before reaching Next.js, are not affected. A patch has been released, `next@12.0.9`, that mitigates this issue. As a workaround, one may ensure `/${locale}/_next/` is blocked from reaching the Next.js instance until it becomes feasible to upgrade.

Affected products

• Vercel Next.js: from 12.0.0, before 12.0.9 (fixed in 12.0.9)

Published 2022-01-28. Last modified 2026-06-17.