The post, part of GitHub Security Lab's series on the OWASP Top 10 Proactive Controls, focuses on the importance of input validation as a secondary defense mechanism for enhancing software security. Input validation ensures that only properly formatted data can enter a software system, helping to mitigate potential vulnerabilities such as injection attacks. The article emphasizes the concept of defense in depth, where multiple layers of security controls provide redundancy to protect against exploitation. It discusses various input validation techniques, including allow lists, deny lists, and the distinction between validation and sanitization, highlighting the strengths and weaknesses of each approach. The post also underscores the necessity of performing server-side validation to ensure security, as client-side validation can easily be bypassed. Additionally, the use of automated tools like static analysis and semantic CodeQL queries in CI/CD pipelines is recommended to enforce validation rules and detect anti-patterns. Overall, input validation is portrayed as a crucial aspect of reducing an application's attack surface, while not being the primary defense against attacks.