What is a common characteristic of zero day vulnerabilities?

A common characteristic of zero-day vulnerabilities is that they remain undetected by most users until exploited. These vulnerabilities refer to security flaws that are unknown to the software vendor or antivirus vendors at the time they are discovered and potentially exploited by attackers. Because there is no prior knowledge or public reporting of the vulnerability, users and organizations are often unaware of the risk until they have been targeted, leading to the term "zero day"—referring to the fact that software developers have had zero days to address or patch the vulnerability since its discovery.

This undetected nature allows them to pose significant risks, as attackers can exploit these flaws without resistance, making them particularly dangerous in the cybersecurity landscape. Once a zero-day vulnerability is discovered, it can take time for vendors to react, and during that time, numerous systems can be compromised if they are not protected by other means.