The attack surface of a system refers to the sum of all potential points where an unauthorized user can try to enter or extract data from that system. It encompasses all the vulnerabilities, including software flaws, unsecured network ports, and unprotected system endpoints. Therefore, when vulnerabilities are decreased, the attack surface is reduced because there are fewer opportunities for an attacker to exploit. This is a fundamental concept in network security, as reducing the attack surface is a critical step in protecting systems against unauthorized access and potential breaches.

References: The explanation aligns with the definitions and concepts of attack surfaces as described in network security literature and the Certified Network Defender (CND) course, which emphasizes the importance of minimizing vulnerabilities to reduce the overall attack surface123.