Next.js is a React framework that can provide building blocks to create web applications. Prior to 13.5.1, an inconsistent interpretation of a crafted HTTP request meant that requests are treated as both a single request, and two separate requests by Next.js, leading to desynchronized responses. This led to a response queue poisoning vulnerability in the affected Next.js versions.

For a request to be exploitable, the affected route also had to be making use of the rewrites feature in Next.js. The vulnerability is resolved in Next.js 13.5.1 and newer.