A software vendor has had several zero-day attacks against its software, due to previously unknown security defects being exploited by attackers. The attackers have been able to perform operations…

Application sandboxing creates a restricted execution environment that confines an application's access to system resources, even when the application is fully compromised. If an attacker exploits an unknown vulnerability, the sandbox prevents them from performing operations at the full security level of the trusted application or underlying OS. This directly addresses the described attack pattern where attackers gained the same privilege level as the application by containing the blast radius of any exploit.

Input validation reduces injection and parsing vulnerabilities but does not restrict the privilege level an attacker can achieve once a zero-day in memory management or application logic is successfully exploited.

Penetration testing is a reactive security assessment technique used to discover existing vulnerabilities, not a software design principle that constrains runtime behavior or privilege escalation.

Code reviews are a quality assurance process that may catch known vulnerability patterns, but they cannot reliably prevent unknown zero-day defects from being introduced or exploited in a live environment.