What does “zero-day vulnerability" refer to?

Correct option is A

• A zero-day vulnerability is a security flaw that is unknown to the software vendor or remains unpatched.
• Attackers exploit it before developers have “zero days” to fix it → hence the name.
• These attacks are high-risk because:
– There is no security update available
– Traditional defenses often cannot detect the exploit
• Zero-day exploits are commonly used in cyber-espionage, Ransomware, APT attacks.