Explanation:
In this question, we have out-of-date applications that could be exploited. The out-of-date applications are security vulnerabilities. The combination of all vulnerabilities that could be exploited (or attacked) is known as the attack surface.

The attack surface of a software environment is the sum of the different points (the “attack vectors”) where an unauthorized user (the “attacker”) can try to enter data to or extract data from an environment. The basic strategies of attack surface reduction are to reduce the amount of code running, reduce entry points available to untrusted users, and eliminate services requested by relatively few users. One approach to improving information security is to reduce the attack surface of a system or software. By turning off unnecessary functionality, there are fewer security risks. By having less code available to unauthorized actors, there will tend to be fewer failures. Although attack surface reduction helps prevent security failures, it does not mitigate the amount of damage an attacker could inflict once a vulnerability is found.