What is a zero-day exploit?

A zero-day exploit refers to the situation where an attacker leverages a vulnerability in software or hardware that is not yet known to the vendor or the public, meaning there is no available fix or patch for it. This vulnerability has "zero days" of protection because it has not been addressed; thus, the window of opportunity for attackers to exploit it remains open until the vendor becomes aware of the issue and releases a fix.

In this context, the correct choice highlights the nature of zero-day exploits as an advance attack on an unpatched flaw, allowing malicious actors to compromise systems, steal information, or conduct other harmful activities before users or developers can defend against it. This characteristic makes zero-day vulnerabilities particularly dangerous in the cybersecurity landscape, as they can lead to significant breaches and security incidents before any countermeasures are implemented.