python network_error ai_generated true

Access to XMLHttpRequest at 'http://api.local/users' from origin 'http://app.local' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

ID: python/flask-cors-no-access-control-origin

Also available as: JSON · Markdown · 中文
80%Fix Rate
84%Confidence
0Evidence
2024-07-07First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
4.x active — — —

Root Cause

Flask-CORS was not initialized, or the origin was not in the allowed list, so the browser blocked the cross-origin response.

generic

中文

未初始化 Flask-CORS，或源不在允许列表中，导致浏览器阻止了跨域响应。

Workarounds

  1. 95% success 
    from flask_cors import CORS
CORS(app, origins=['http://app.local'], supports_credentials=True)
  2. 80% success 
    @app.route('/users', methods=['GET','OPTIONS'])
def users(): ...

Dead Ends

Common approaches that don't work:

  1. 85% fail

    Preflight OPTIONS requests still fail, so POST/PUT never reach the server.

  2. 90% fail

    Browsers reject wildcard origins when credentials are included.