Insider threats and zero-day attacks are two of the most elusive and damaging forms of cyber threats. Insider threats emerge when individuals within an organization misuse their authorized access, either maliciously or negligently, to compromise security. On the other hand, zero-day attacks exploit previously unknown software vulnerabilities, leaving systems exposed until patches can be deployed. While researchers often address these attack vectors independently, their convergence poses a uniquely complex and stealthy security challenge. This analytical review explores how malicious insiders can facilitate or exploit zero-day vulnerabilities and how compromised insider accounts can act as conduits for sophisticated zero-day exploits. By examining real-world case studies, this review sheds light on how zero-day flaws can be discovered, shared, or weaponized from within an organization—often bypassing perimeter defenses and evading traditional detection methods. In addition to illustrating how this convergence can remain undetected, the paper discusses broad strategies for mitigation and prevention, including advanced threat intelligence, anomaly detection, behavior analytics, and improved patch management processes. The review concludes by emphasizing the importance of a multifaceted, proactive security policy that accounts for internal and external risks and incorporates emerging technologies, organizational policies, and cross-industry collaboration to strengthen resilience against insider-enabled zero-day attacks.