It's used a lot in the data heavy AI world for it's efficiency shipping large files. This includes lots and lots of production servers.
From the advisory: 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.
An attacker can send a crafted request like GET /protected with a Host: example.com/health?x= header. The request will reach the /proteced path, but request.url would be https://example.com/health?x=/protected, and request.url.path would return /health instead of the real request path.
They should be stopping this attack at the door (even if only to clean out your logs from scraper door knocks), which is probably why it went unnoticed for years. I don't think anyone would be deploying {A,W}SGI servers on public facing ports these days. Even if only because SSL termination is much easier in the proxy layer.
Also good lord that ARS article is a mess. What the hell happened there? An ASGI server isn't unique to AI or anything, it's just a regular supply chain dependency. I kinda expect better from ARS on stuff like this.
As an example, I just confirmed that both Cloudflare and AWS ALBs reject all of the attack patterns. Still not good, lateral movement is a time-honored tactic, etc. but it buys time to patch.
If you do async python I strongly recommend it.
FastAPI is built on Starlette - to be honest I don’t see the point of the extra baggage - just use Starlette.
function name becomes a human readable summary, string docs the description
edit: bottle.py and fastapi are the most significant contributions to web frameworks in python — decorators for path handlers, typed input/output, automatic docs