Next.js Vulnerable to HTTP Request Smuggling

Impact

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.

Patches

The vulnerability is resolved in Next.js 13.5.1 and newer. This includes Next.js 14.x.

Workarounds

There are no official workarounds for this vulnerability. We recommend that you upgrade to a safe version.

References

https://portswigger.net/web-security/request-smuggling/advanced/response-queue-poisoning