Is it safe to accept URL parameters for populating the `url_for` method?

Question

I am using Ruby on Rails 4.1.1 and I am thinking to accept parameters (through URL query strings) that are passed directly to the url_for method, this way:

Answer 1

This it is safe internally as Ruby On Rails will only be issuing a HTTP redirect response.

As you are using only_path this will protect you from an Open redirect vulnerability. This is where an email is sent by an attacker containing a link in the following format (say your site is example.com).

https://example.com?foo=bar&bar=foo&redirect=http://evil.com

As the user checks the URL and sees it is on the example.com domain they beleive it is safe so click the link. However, if there's an open redirect then the user ends up on evil.com which could ask for their example.com password without the user noticing.

Redirecting to a relative path only on your site fixes any vulnerability.

In your case you are giving users control of your controller, action and parameters. As long as your GET methods are safe (i.e. no side-effects), an attacker could not use this by creating a crafted link that the user opens.

In summary, from the information provided I don't see any risk from phishing URLs to your application.