zero-day

adjective

ze·​ro-day ˈzir-(ˌ)ō-ˈdā 

ˈzē-(ˌ)rō-

computing

: of, relating to, or being a vulnerability (as in a computer or computer system) that is discovered and exploited (as by cybercriminals) before it is known to or addressed by the maker or vendor

Thus, in the parlance of the trade, these vulnerabilities are known as "zero-day exploits," because it has been zero days since they have been uncovered and fixed.

—James Bamford

There's a zero-day vulnerability in RealPlayer and Internet Explorer that allows malicious code to be installed …

—Mark Hopkins

… most of what's on the black market doesn't have that zero-day freshness. Criminals typically target older vulnerabilities, for which fixes have already been released …

—Lev Grossman

Examples of zero-day in a Sentence

Recent Examples on the Web

Microsoft’s monthly Patch Tuesday security update might have been and gone, but Exploit Wednesday could linger for those users who have not been quick enough to protect their systems against a bunch of zero-day vulnerabilities. —Davey Winder, Forbes, 12 Oct. 2024

In addition, current processes may have vulnerabilities that are exploited by attackers before clients and vendors know about them, which are called zero-day exploits. —Margarita Simonova, Forbes, 19 Sep. 2024

Microsoft suggests the culprits may have paid for details about the zero-day exploit from other hackers, citing one such sale of an ESXi exploit that went for $1.5 million. —Michael Kan, PCMAG, 30 July 2024

In the past 17 months, threat actors backed by the North Korean government have targeted developers twice, one of those using a zero-day vulnerability. —Dan Goodin, Ars Technica, 15 July 2024

Word History

First Known Use

2000, in the meaning defined above