A Server-Side Request Forgery (SSRF) vulnerability exists in the POST /worker_generate_stream API endpoint of the Controller API Server in lm-sys/fastchat, as of commit e208d5677c6837d590b81cb03847c0b9de100765. This vulnerability allows attackers to exploit the victim controller API server's credentials to perform unauthorized web actions or access unauthorized web resources by combining it with the POST /register_worker endpoint.