Rule Definition
Exploitation of Excessive Data Exposure is simple, and is usually performed by sniffing the traffic to analyze the API responses, looking for sensitive data exposure that should not be returned to the user. Since APIs are used as data sources, sometimes developers try to implement them in a generic way without thinking about the sensitivity of the exposed data. When binding data fields accessed by APIs to columns it must be cautiously controlled that what data is to be ignored when returning the field or the model

Remediation
Implement a schema-based response validation mechanism as an extra layer of security. As part of this mechanism define and enforce data returned by all API methods, including errors.

https://github.com/OWASP/API-Security/blob/master/2019/en/src/0xa3-excessive-data-exposure.md https://owasp.org/www-project-api-security/