noun
zero-day attack
A cyberattack that exploits a previously unknown vulnerability, for which no patch exists. Used in IT security contexts.
そのゼロデイ攻撃は、多くの企業に深刻な被害をもたらした。
That zero-day attack caused serious damage to many companies.
From English 'zero-day attack'. The term refers to the fact that developers have had zero days to fix the vulnerability.