CORS is not effective to restrict access

[SedatDe]

Describe the bug

If I mount gradio app on FastAPI, and use CORSMiddleware from FastAPI, it does not seem to apply restriction. It just reflects given origin header of request in access-control-allow-origin of response header . However, if I use just a FastAPI route rather than a gradio app, this does not happen.

Have you searched existing issues? 🔎

• I have searched and found no existing issues

Reproduction

Here is the gradio mounted example (example-1):

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
import gradio as gr
import uvicorn

app = FastAPI()
app.add_middleware(
    CORSMiddleware,
    allow_origins=["https://example.com"]
)

with gr.Blocks() as demo:
    gr.Textbox("hello")
    
app = gr.mount_gradio_app(app, demo, path="/")
uvicorn.run(app, host="0.0.0.0", port=55800)

Here is the pure FastAPI example (example-2):

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
import uvicorn

app = FastAPI()
app.add_middleware(
    CORSMiddleware,
    allow_origins=["https://example.com"]
)

@app.get("/")
async def root():
    return {"message": "Hello"}

uvicorn.run(app, host="0.0.0.0", port=55800)

If I make a request with the following

curl -i http://10.255.83.104:55800/ -H "Origin: https://malicious.com"

Example-1 returns access-control-allow-origin with whatever is given in origin header.

HTTP/1.1 200 OK
date: Thu, 02 Jan 2025 10:44:18 GMT
server: uvicorn
content-length: 4097
content-type: text/html; charset=utf-8
access-control-allow-credentials: true
access-control-allow-origin: https://malicious.com
vary: Origin

Example-2 does not return access-control-allow-origin, namely applies the expected restriction.

HTTP/1.1 200 OK
date: Thu, 02 Jan 2025 10:43:48 GMT
server: uvicorn
content-length: 19
content-type: application/json

Screenshot

No response

Logs

No response

System Info

Operating System: Linux
gradio version: 5.7.1
gradio_client version: 1.5.0

Severity

Blocking usage of gradio

[abidlabs]

Hi @SedatDe the reason for this is that Gradio includes its own cors middleware which behaves as you described. Perhaps you can get around this by mounting your cors middleware after mounting the gradio app -- can you try this?

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
import gradio as gr
import uvicorn

app = FastAPI()

with gr.Blocks() as demo:
    gr.Textbox("hello")
    
app = gr.mount_gradio_app(app, demo, path="/")

app.add_middleware(
    CORSMiddleware,
    allow_origins=["https://example.com"]
)

uvicorn.run(app, host="0.0.0.0", port=55800)

[SedatDe]

Hi @abidlabs thank you for your quick response.
I tried your suggestion, but I still get access-control-allow-origin: https://malicious.com response header.