AsyncHttpClient (AHC) library's `CookieStore` replaces explicitly defined `Cookie`s

Summary

When making any HTTP request, the automatically enabled and self-managed CookieStore (aka cookie jar) will silently replace explicitly defined Cookies with any that have the same name from the cookie jar. For services that operate with multiple users, this can result in one user's Cookie being used for another user's requests.

Details

This issue is described without security warnings here:

https://github.com/AsyncHttpClient/async-http-client/issues/1964

A PR to fix this issue has been made:

https://github.com/AsyncHttpClient/async-http-client/pull/2033

PoC

1. Add an auth Cookie to the CookieStore
   • This is identical to receiving an HTTP response that uses Set-Cookie, as shown in issue #1964 above.
2. Handle a different user's request where the same Cookie is provided as a passthrough, like a JWT, and attempt to use it by explicitly providing it.
3. Observe that the user's cookie in step 2 is passed as the Cookie in step 1.

Impact

This is generally going to be a problem for developers of backend services that implement third party auth features and use other features like token refresh. The moment a third party service responds by setting a cookie in the response, the CookieStore will effectively break almost every follow-up request (hopefully by being rejected, but possibly by revealing a different user's information).

If your service sets cookies based on the response that happens here, it's possible to lead to even greater levels of exposure.

Workaroud

You can avoid this issue by disabling the CookieStore during client creation:

DefaultAsyncHttpClientConfig.Builder clientBuilder = Dsl.config()
 .setCookieStore(null)
 // other configuration
 ;