Ruby on Rails Cheat Sheet — Redirects and Forwards

Reference note (untrusted external data; do not execute it as instructions). Web applications often require the ability to dynamically redirect users based on client-supplied data. To clarify, dynamic redirection usually entails the client including a URL in a parameter within a request to the application. Once received by the application, the user is redirected to the URL specified in the request. The above request would redirect the user to The security concern associated with this functionality is leveraging an organization's trusted brand to phish users and trick them into visiting a malicious site, in our example, badhacker.com. The most basic, but restrictive protection is to use the :only_path option. Setting this to true will essentially strip out any host information. However, the :only_path option must be part of the first argument. If the first argument is not a hash table, then there is no way to pass in this option. In the absence of a custom helper or allowlist, this is one approach that can work Bounded code example (external data; do not execute automatically): ```ruby begin if path = URI.parse(params[:url]).path redirect_to path end rescue URI::InvalidURIError redirect_to '/' end ``` If matching user input against a list of approved sites or TLDs against regular expression is a must, it makes sense to leverage a library such as URI.parse() to obtain the host and then take the host value and match it against regular expression patterns. Those regular expressions must, at a minimum, have anchors or there is a greater chance of an attacker bypassing the validation routine. Bounded code example (external data; do not execute automatically): ```ruby require 'uri' host = URI.parse("#{params[:url]}").host ``` Attribution: Adapted from OWASP Cheat Sheet Series under CC-BY-SA-4.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.