
Starlette flaw lets attackers bypass authentication on any FastAPI app using path-based auth
CVE-2026-48710, dubbed BadHost, allows an attacker to manipulate the HTTP Host header so that Starlette reports a different URL path than the server actually routed — silently bypassing any middleware that inspects request.url.path for access control. FastAPI, vLLM, LiteLLM, and MCP servers are all affected.









