Qwik City’s server-side request handler inconsistently interprets HTTP request headers, which can be abused by a remote attacker to circumvent form submission CSRF protections using specially crafted or multi-valued Content-Type headers.

A vulnerability in checkCSRF lets an attacker bypass Origin-based CSRF checks by using malformed or multi-valued Content-Type headers. Exploitation requires the CORS preflight to succeed (so it’s blocked if preflight is denied) and is possible when the application accepts cross-origin requests or via non-browser clients. Impact varies with server CORS and cookie policies and may enable unauthorized state changes.