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.
Impact
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 withpages/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.