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

Not much is known about the vulnerability itself, as is often the case with such zero-day issues this detail is held back until as many users as possible have had the opportunity to patch against the exploit. —Davey Winder, Forbes, 12 Dec. 2024

Meanwhile, the Windows zero-day, CVE‑2024‑49039, rated at 8.8 out of 10, was a privilege of escalation flaw that could enable malicious code to operate outside of the Mozilla Firefox browser security sandbox. —Davey Winder, Forbes, 30 Nov. 2024

There still remains a separate issue, of course, with Qualcomm’s zero-day patch from last month not making it into Samsung’s November release—unlike Pixels. —Zak Doffman, Forbes, 20 Nov. 2024

These elite hackers and security researchers work relentlessly to uncover zero-day vulnerabilities in Google’s products and beyond. —Davey Winder, Forbes, 5 Nov. 2024

Word History

First Known Use

2000, in the meaning defined above