Possible Information Disclosure / Unintended Method Execution in Action Pack

There is a possible information disclosure / unintended method execution
vulnerability in Action Pack which has been assigned the CVE identifier
CVE-2021-22885.

Versions Affected: >= 2.0.0.
Not affected: < 2.0.0.
Fixed Versions: 6.1.3.2, 6.0.3.7, 5.2.4.6, 5.2.6

Impact

There is a possible information disclosure / unintended method execution
vulnerability in Action Pack when using the redirect_to or polymorphic_url
helper with untrusted user input.

Vulnerable code will look like this:

redirect_to(params[:some_param])

All users running an affected release should either upgrade or use one of the
workarounds immediately.

Workarounds

To work around this problem, it is recommended to use an allow list for valid
parameters passed from the user. For example:

private def check(param)
  case param
  when "valid"
    param
  else
    "/"
  end
end

def index
  redirect_to(check(params[:some_param]))
end

Or force the user input to be cast to a string like this:

def index
  redirect_to(params[:some_param].to_s)
end