ccb.belgium.beadvisory

Warning: Vulnerability in Starlette framework and related frameworks like FastAPI exposes millions of servers to authentication bypass, Patch Immediately! | CCB Belgium

Belgian CCB advisory on CVE-2026-48710 ("BadHost", CVSS 6.5), an authentication bypass in Starlette versions before 1.0.1. The Host header was not validated when request.url was rebuilt, so request.url.path could differ from the routed path. Middleware and endpoints that enforce access control on request.url could therefore be bypassed. The flaw affects FastAPI, LiteLLM, vLLM, MCP servers and other Python LLM infrastructure, and may expose stored third-party credentials. The advisory recommends upgrading to 1.0.1 or later and increasing monitoring, and links to the badhost.org scanner and to the GitHub, OSTIF, X41 D-Sec and Ars Technica write-ups.