CVE-2026-48710 Starlette Host-Header Auth Bypass

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security-vulnerability cve starlette fastapi auth-bypass host-header asgi

Summary

A critical host-header authentication bypass vulnerability (CVE-2026-48710) in Starlette and FastAPI affects many Python ASGI applications, including AI inference servers (e.g., vLLM), AI proxy servers (e.g., LiteLLM), and MCP gateways, potentially allowing unauthorized access.

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Cached at: 05/27/26, 09:30 AM

# BadHost - CVE-2026-48710 Starlette Host-Header Auth Bypass Source: [https://badhost.org/](https://badhost.org/) Any Python application built on Starlette or FastAPI that uses`starlette < 1\.0\.1`and uses`request\.url`\(or`starlette\.datastructures\.URL\(scope=\.\.\.\)`\) in a middleware to make security decisions based on its`path`\(e\.g\. allowlists, denylists, CSRF exemptions, rate limiting, payment gates\), and runs on any ASGI server \(Daphne, Granian, Gunicorn, Hypercorn, Anycorn, Uvicorn\)\. Use the scanner above, grep your codebase for`request\.url\.path`in middleware files, or try the tools from the[X41 open\-source repository](https://github.com/x41sec/poc/tree/master/starlette-host-header)\. This includes LLM inference servers like vLLM, LLM proxy servers like LiteLLM, AI agent frameworks, MCP gateways, and custom APIs\. MCP servers are especially at risk because the MCP spec mandates unauthenticated OAuth discovery endpoints, providing a reliable path for exploitation

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