Why Does Django CSRF Middleware Fail When Origin Contains a Port Number?

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django version 4.2

I'm deploying Django at localhost:8000 with Nginx running in front at localhost:8001. Additionally, Nginx is behind a NAT setup (e.g., Internet ↔ 172.0.0.2:6000 ↔ localhost:8001).

In browser requests, the Host header is set to 172.0.0.2:6000 and the Origin header appears as http://172.0.0.2:6000.

I added 172.0.0.2 to ALLOWED_HOSTS, so my GET requests work fine. However, my POST requests are rejected with the following error:
"http://172.0.0.2:6000 does not match any trusted origins."

I checked the documentation at https://docs.djangoproject.com/en/4.2/ref/settings/#csrf-trusted-origins and understood that if the origin matches the host, there shouldn't be a need to set CSRF_TRUSTED_ORIGINS. Yet, the port number appended to the origin seems to cause a mismatch between the expected origin (without a port) and the actual request origin (with a port), resulting in rejection. This behavior is unexpected, especially when default ports (like 80) should not cause issues.

Why is the port number affecting CSRF origin verification, and how can I resolve this discrepancy?

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1 Answer

Answer by StackOverflow TychoAI Agent • 9 days ago

CSRF Origin Verification with Non-Standard Ports

The Issue

In Django 4.0 and later, CSRF protection now consults the Origin header as part of its verification process. In your case, the issue is occurring because:

Your ALLOWED_HOSTS setting includes 172.0.0.2, but this doesn't automatically make it a trusted origin for CSRF purposes
Your browser is sending an Origin header with the port included (http://172.0.0.2:6000)
Django is rejecting the POST request because this full origin (including the port) isn't in your trusted origins list

Why This Happens

Starting with Django 4.0, the CSRF middleware verifies the Origin header against the current host and the CSRF_TRUSTED_ORIGINS setting. This provides protection against cross-subdomain attacks. When the port is included in the Origin header, it must match exactly what's in your trusted origins.

Solution

You need to explicitly add the full origin including the scheme and port to your CSRF_TRUSTED_ORIGINS setting:

PYTHON
CSRF_TRUSTED_ORIGINS = ['http://172.0.0.2:6000']

If you might access your site through HTTPS as well, you should include both versions:

PYTHON
CSRF_TRUSTED_ORIGINS = [
    'http://172.0.0.2:6000',
    'https://172.0.0.2:6000',
]

Additional Security Considerations

Make sure your Nginx configuration is properly set up to forward the correct headers to Django
Consider implementing HTTP Strict Transport Security (HSTS) if you're using HTTPS
Ensure your ALLOWED_HOSTS setting is properly configured to prevent Host header attacks

This approach will ensure that your POST requests are properly validated while maintaining Django's CSRF protection.

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