Which of the following is most likely to pose a security threat to a web server?

CGI scripts pose a significant security threat to a web server primarily because they are executable scripts that can interact with the server's backend and the operating system. When improperly configured or if they contain vulnerabilities, these scripts can be exploited by attackers, leading to issues such as command injection, buffer overflows, or unauthorized access to server resources.

The potential for risks increases because CGI scripts often handle input data from users, which can be manipulated to perform attacks. Additionally, if security measures are not adequately implemented, such as input validation and output encoding, the risk of exploitation rises significantly.

While other options may present risks, such as database connections if poorly managed, or issues related to legacy technologies like Flash, CGI scripts are particularly notorious for being entry points for various attacks due to their direct execution on the server. This makes them a prominent concern in web security protocols and practices, reinforcing the need for stringent security practices around their deployment and management.