stimulus_reflex is a system to extend the capabilities of both Rails and Stimulus by intercepting user interactions and passing them to Rails over real-time websockets. In affected versions more methods than expected can be called on reflex instances. Being able to call some of them has security implications. To invoke a reflex a websocket message of the following shape is sent: "\"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. This is problematic as "reflex.method method_name" can be more methods that those explicitly specified by the developer in their reflex class. A good example is the instance_variable_set method. This vulnerability has been patched in versions 3.4.2 and 3.5.0.rc4. Users unable to upgrade should: see the backing GHSA advisory for mitigation advice.