Implementing input validation is the correct measure to ensure that the size and type of user input is checked before processing. This control prevents attackers from exploiting buffer vulnerabilities by inputting data that can lead to buffer overflows. Input validation is a fundamental security control for protecting against various types of input-based vulnerabilities such as buffer overflows, SQL injections, and cross-site scripting. The other options, while important in their own right, do not directly address the issue of ensuring that input does not exceed buffer capacity or contain malicious data.