Improper Handling of Unexpected Data Type

At its core, this weakness is about broken assumptions in your code's data handling. Developers often write logic expecting data in a specific format—like integers, strings, or structured objects. When the incoming data doesn't match that type (e.g., a user submits 'abc' where a number is required), the application may throw unhandled exceptions, behave unpredictably, or expose internal system details through error messages. To prevent this, implement strict input validation and type checking at all system boundaries. Use strong typing in your programming language where possible, and always sanitize and verify data from external sources like user inputs, APIs, or files before processing. Defensive coding practices, such as using try-catch blocks and designing functions to handle a range of input types gracefully, are essential to maintain stability and security when faced with unexpected data.