Angular / Flask app failing with CORS error after upgrading to macOS Sequoia

I just upgraded to Sequoia and I’m having some odd issues.

I have an Angular app which runs a Flask backend. They live in the same directory and I map the Flask app (port 5000) as the api for the Angular app (port 4200).

.
├── backend <-- Flask code
├── frontend <-- Angular code
├── node_modules
├── package-lock.json
├── package.json
├── README.md
└── requirements.txt


It’s been running great for like 9 months. But now when I try to load the site, the API layer keeps complaining about CORS permissions.

Access to XMLHttpRequest at ‘http://localhost:5000/api/exports/vendors’ from origin ‘http://localhost:4200’ has been blocked by CORS policy: No ‘Access-Control-Allow-Origin’ header is present on the requested resource.


I’ve already got a Python package which allows for CORS. And as I said, this has been working perfectly as recently as 4 days ago (my last commit).

api = Blueprint('api', __name__, url_prefix='/api')
app = Flask(__name__, static_folder='../frontend/dist/mmscripts/browser/', static_url_path='')
CORS(app)


While I debug this locally, can anyone think of anything that might have changed with this new OS that might be cause this? This could be related (and I could be an idiot), but I can visit http://localhost:4200/ to view the Angular app, but http://127.0.0.1:4200/ fails. I can load http://localhost:5000/ to view the Flask served version of this app (but it has no hot reloading).

I’m just baffled why this is failing all of a sudden.

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