A zero-day exploit is an attack technique that targets a software or hardware vulnerability unknown to the vendor and for which no patch yet exists, giving defenders zero days to prepare. Because the flaw is undisclosed, such exploits bypass signature-based defenses and are highly valuable to attackers, state actors, and exploit brokers. They matter as a central concern in cybersecurity, surveillance, and offensive cyber operations.
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- Because no signature or fix exists, zero-days evade conventional detection and command high prices on grey and black markets, where they are stockpiled by intelligence agencies and offensive-security firms. Defenders counter them with behavioural anomaly detection, sandboxing, exploit mitigations, and rapid coordinated disclosure once a flaw surfaces.