Vulnerability Instance

CSRF Vulnerability in rails-ujs
There is a vulnerability in rails-ujs that allows attackers to send CSRF tokens to wrong domains.

Versions Affected:  rails <= 6.0.3
Not affected:       Applications which don't use rails-ujs.
Fixed Versions:     rails >= 5.2.4.3, rails >= 6.0.3.1

Impact
------

This is a regression of CVE-2015-1840.

In the scenario where an attacker might be able to control the href attribute of an anchor tag or the action attribute of a form tag that will trigger a POST action, the attacker can set the href or action to a cross-origin URL, and the CSRF token will be sent.

Workarounds
-----------

To work around this problem, change code that allows users to control the href attribute of an anchor tag or the action attribute of a form tag to filter the user parameters.

For example, code like this:

    link_to params

to code like this:

    link_to filtered_params

    def filtered_params
      # Filter just the parameters that you trust
    end