TLDR: Misconfigured CORS (Cross-Origin Resource Sharing), introduced in 2009, can expose web applications to security vulnerabilities such as unauthorized data access, session hijacking, and data leakage. Issues like overly permissive origins, insecure methods, or improper handling of credentials undermine the purpose of CORS, which is to securely manage cross-origin requests.

https://en.wikipedia.org/wiki/Cross-origin_resource_sharing

One frequent issue with CORS misconfiguration is the use of wildcard origins (`*`) in the `Access-Control-Allow-Origin` header, which permits any domain to access sensitive resources. Similarly, failing to restrict `Access-Control-Allow-Methods` to only necessary HTTP methods, such as `GET` or `POST`, can allow dangerous actions like `DELETE` or `PUT`. Another problem arises when credentials, such as cookies or authentication headers, are unnecessarily exposed by setting `Access-Control-Allow-Credentials: true` without proper origin restrictions.

https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS

To mitigate these risks, developers should explicitly define trusted origins and limit the methods and headers allowed in cross-origin requests. Using dynamic CORS configurations based on verified request sources further tightens security. Testing tools like Postman or curl help verify the effectiveness of CORS rules. Proper configuration, regular audits, and adherence to CORS best practices ensure secure and efficient cross-origin communication.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Allow-Origin