- Published on
CORS
- Authors
- Name
- Bowen Y
What will happen if I allow localhost in CORS policy?
When you allow http://localhost:3000
in your CORS policy, anyone running a frontend on http://localhost:3000
on their own machine will be able to make requests to your backend service. Here's how it works:
CORS and Localhost: The
http://localhost:3000
you allow in your CORS policy refers to any instance of a service running on port 3000 onlocalhost
. Thislocalhost
is specific to the computer that the service is running on.Different People, Different
localhost
: If multiple people run frontend services on their ownlocalhost:3000
, they are running those services on their own machines. Therefore, if your backend service allows requests fromhttp://localhost:3000
, it will accept requests from any frontend running atlocalhost:3000
on any machine.
Key Point:
Not Limited to Your Machine: Allowing
http://localhost:3000
in CORS does not limit requests to just your machine. It means that any machine with a service running athttp://localhost:3000
can make cross-origin requests to your backend service.So, if someone else runs a frontend on their own computer at
http://localhost:3000
, and your backend allows requests fromhttp://localhost:3000
, their frontend can access your backend service.
Example:
- Your Development Setup: You may allow
http://localhost:3000
in CORS because your frontend is running locally atlocalhost:3000
and you want it to communicate with your backend. - Another Developer's Setup: Another person on their own computer could also run a frontend at
http://localhost:3000
. If your backend is publicly accessible and allows requests fromhttp://localhost:3000
, their frontend could also make requests to your backend.
Important Considerations:
- Backend Authentication: While CORS allows cross-origin requests, it doesn't handle authentication. Even if someone can send requests to your backend from
http://localhost:3000
, your backend should still have proper authentication and authorization mechanisms to control access. - Local Development vs. Production: Typically, allowing
localhost
in CORS is for development purposes. In production, you would restrict CORS to trusted domains (e.g., your deployed frontend's domain) to prevent unintended access.
In summary, allowing http://localhost:3000
in CORS means that anyone running a service on their own localhost:3000
can access your backend, not just you on your own machine.