What is the definition of a zero-day exploit?

A zero-day exploit is fundamentally defined as a security vulnerability that is unknown to the software vendor and has not yet been patched. This term originates from the fact that when a vulnerability is discovered, the software creator has “zero days” to fix the issue before it is potentially exploited by attackers. This characteristic makes zero-day exploits especially dangerous, as they can be used to compromise systems or steal sensitive information before a remedy is developed and deployed.

Recognizing the nature of zero-day exploits helps underscore the importance of proactive security measures, such as regular software updates and vulnerability assessments, to minimize the risk of such unaddressed weaknesses being exploited. In contrast to the other options, which reference unrelated concepts like phishing attacks or firewall settings, the definition accurately captures the urgency and severity associated with this particular type of vulnerability.