The vulnerability stems from missing CSRF protection middleware rather than specific vulnerable functions. The patch added Rack::Protection and session management (Rack::Session::Pool) at the application level in lib/geminabox/server.rb. The vulnerability existed because the application didn't implement CSRF tokens or protection mechanisms for state-changing operations like gem uploads. While the gem upload handler (likely in the Server class) was the attack vector, the root cause was the absence of CSRF protection across all routes, not a flaw in specific function implementations. The fix addressed this through middleware configuration rather than modifying individual functions.