CVE-2021-43803: Vercel Next.js

High severity, CVSS 7.5. EPSS: 47.3% chance of exploitation in the next 30 days.

Next.js is a React framework. In versions of Next.js prior to 12.0.5 or 11.1.3, invalid or malformed URLs could lead to a server crash. In order to be affected by this issue, the deployment must use Next.js versions above 11.1.0 and below 12.0.5, Node.js above 15.0.0, and next start or a custom server. Deployments on Vercel are not affected, along with similar environments where invalid requests are filtered before reaching Next.js. Versions 12.0.5 and 11.1.3 contain patches for this issue.

Affected products

• Vercel Next.js: from 11.1.0, before 11.1.3 (fixed in 11.1.3); from 12.0.0, before 12.0.5 (fixed in 12.0.5)

Published 2021-12-10. Last modified 2026-06-17.