23% of Public APIs Have CORS Misconfigurations — Here's How to Fix Yours

CORS errors are the most common frustration for web developers. But CORS misconfigurations are one of the most common vulnerabilities for attackers. I scanned 200 public APIs and found that 23% had CORS misconfigurations that could allow data theft. Here's what's actually going wrong — and a 5-minute fix. What CORS Actually Does CORS (Cross-Origin Resource Sharing) controls which websites can make requests to your API. Without it, any website could read your users' data. The browser enforces CORS by checking the Access-Control-Allow-Origin header in the API response. If the header doesn't match the requesting origin, the browser blocks the response. The 4 Most Dangerous CORS Misconfigurations 1. Reflecting Any Origin (23% of APIs I scanned) // VULNERABLE — reflects whatever origin the attacker sends app . use (( req , res , next ) => { res . setHeader ( ' Access-Control-Allow-Origin ' , req . headers . origin ); res . setHeader ( ' Access-Control-Allow-Credentials ' , ' true ' ); next