docs/warning_types/redirect/index.markdown
Unvalidated redirects and forwards are #10 on the [OWASP Top Ten](https://www.owasp.org/index.php/Top_10_2010-A10).
Redirects which rely on user-supplied values can be used to "spoof" websites or hide malicious links in otherwise harmless-looking URLs. They can also allow access to restricted areas of a site if the destination is not validated.
Brakeman will raise warnings whenever `redirect_to` appears to be used with a user-supplied value that may allow them to change the `:host` option.
For example,
redirect_to params.merge(:action => :home)
will create a warning like
Possible unprotected redirect near line 46: redirect_to(params)
This is because `params` could contain `:host => 'evilsite.com'` which would redirect away from your site and to a malicious site.
If the first argument to `redirect_to` is a hash, then adding `:only_path => true` will limit the redirect to the current host. Another option is to specify the host explicitly.
redirect_to params.merge(:only_path => true)
redirect_to params.merge(:host => 'myhost.com')
If the first argument is a string, then it is possible to parse the string and extract the path:
redirect_to URI.parse(some_url).path
If the URL does not contain a protocol (e.g., `http://`), then you will probably get unexpected results, as `redirect_to` will prepend the current host name and a protocol.