What is a zero-day vulnerability?

A zero-day vulnerability refers to a flaw that is unknown to the software vendor or the organization responsible for the application's security. Since the vendor has not identified or patched this vulnerability, it can be exploited by attackers, posing significant risks. The term "zero-day" emphasizes that there are zero days of protection available to the vendor or users against potential attacks that leverage this vulnerability.

This type of vulnerability is particularly dangerous because it can be actively targeted by hackers before the vendor has an opportunity to develop and release a fix, leaving systems exposed. Cybersecurity measures typically focus on reducing the risk of zero-day vulnerabilities by employing strategies such as intrusion detection systems, behavioral analysis, and maintaining a robust patch management process for known vulnerabilities.

In contrast, the other options describe situations involving vulnerabilities that are known and can be addressed, such as patched flaws or weaknesses identified through user training, which do not encompass the nature of zero-day vulnerabilities.