Which aspect of security does zero-day protection directly address?

Zero-day protection specifically targets vulnerabilities that have recently been discovered but for which no patch or fix is currently available. These vulnerabilities are termed "zero-day" because they are exploited on or before the day that developers become aware of them, leaving no time for protective measures or fixes to be implemented.

When attackers exploit these unpatched vulnerabilities, they can potentially gain unauthorized access or cause harm to systems before any defensive measures can be employed. Zero-day protection employs various security measures, such as threat detection and behavioral analysis, to identify and mitigate attacks exploiting these vulnerabilities in real-time.

In contrast, the other aspects of security mentioned do not directly pertain to zero-day threats. For instance, protection against previously known vulnerabilities would involve patching systems to address vulnerabilities that are already known and for which updates exist. Advanced persistent threats refer to a different category of long-term, targeted attacks often involving sophisticated methods beyond just exploiting a single vulnerability. Content filtering typically deals with controlling what data can enter or exit a network, rather than addressing vulnerabilities directly.