An API vulnerability is a security flaw or weakness within an Application Programming Interface (API) that can be exploited by attackers. These vulnerabilities may allow unauthorized access, data leakage, manipulation of data, or even complete system compromise. Common issues include insufficient authentication, lack of input validation, and improper error handling. As APIs are widely used to connect services and transfer data, vulnerabilities can have significant impacts, such as exposing sensitive information or enabling malicious actions. Regular security assessments, proper coding practices, and robust authentication mechanisms are crucial to mitigate API vulnerabilities and protect digital assets.