Summary More methods than expected can be called on reflex instances. Being able to call some of them has security implications. Details To invoke a reflex a websocket message of the following shape is sent: json { "target": "[class_name]#[method_name]", "args": [] } The server will proceed to instantiate reflex using the provided class_name as long as it extends StimulusReflex::Reflex. It then attempts to call method_name on the instance with the provided arguments ref: “`ruby method = reflex.method method_name required_params = method.parameters.select { |(kind, )| kind == :req } optional_params = method.parameters.select { |(kind, )| kind == :opt } if arguments.size >= required_params.size && arguments.size <= required_params.size + optional_params.size reflex.public_send(method_name, *arguments) end “` This is problematic as reflex.method(method_name) can be more methods than those explicitly specified by the developer in their reflex class. A good example is the instance_variable_set method. json { "target": "StimulusReflex::Reflex#render_collection", "args": [ { "inline": "<% system('[command here]') %>" } ] } Patches Patches are available on RubyGems and on NPM. The patched versions are: – 3.4.2 – 3.5.0.rc4 Workaround You can add this guard to mitigate the issue if running an unpatched version of the library. 1.) Make sure all your reflexes inherit from the ApplicationReflex class 2.) Add this before_reflex callback to your…Read More