Which solution should be deployed to block SQL injection attacks on a web application?

Deploying a Web Application Firewall (WAF) is the most effective solution to block SQL injection attacks on a web application. A WAF is specifically designed to monitor, filter, and control HTTP traffic to and from a web application. By doing so, it can detect and block malicious requests that attempt to exploit vulnerabilities in the application, such as those associated with SQL injection.

SQL injection attacks occur when an attacker is able to manipulate a web application's database queries through specially crafted input. A WAF can analyze this input in real-time and apply predefined rules and security policies to identify and mitigate risky queries before they reach the backend database. Moreover, a WAF often includes capabilities to block or sanitize input data, provide detailed logging for audit purposes, and issue alerts on suspicious activity.

In contrast, other options like a Virtual Private Network (VPN) or Secure Socket Shell (SSH) primarily focus on securing communications between networks or securing remote access, leaving web applications vulnerable to SQL injection risks. Security Information and Event Management (SIEM) systems are valuable for incident detection and analysis but do not actively block web application threats in real-time. Thus, utilizing a WAF is the most direct and effective approach to protecting against SQL injection attacks.