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 On the plus side, Google noticed financially motivated cybercriminals exploiting only 10 zero-day vulnerabilities, a drop from 2022. —

Michael Kan, PCMAG, 27 Mar. 2024 Out of these 97 zero-day vulnerabilities, 29 were originally discovered by Google’s security researchers. —

Davey Winder, Forbes, 27 Mar. 2024 Sophisticated Cyber Threats: Advanced and sophisticated cyberattacks—including ransomware, phishing and zero-day exploits—require robust defense mechanisms. —

Mike Kijewski, Forbes, 23 Feb. 2024 Traditional cybersecurity approaches—including firewalls, antivirus software, and intrusion detection systems—are frequently outpaced by sophisticated threats like polymorphic malware and zero-day exploits. —

Kunle Fadeyi, Forbes, 15 Feb. 2024 Unit 42 said the uptick was due to the massive impact of attacks that exploited zero-day vulnerabilities, which are security flaws that developers have yet to identify. —

Lauren Feiner, The Verge, 5 Feb. 2024 The eighth zero-day vulnerability impacting Chrome in 2024, CVE-2023-7024 is a heap buffer overflow issue in the open source WebRTC component. —

Kate O'Flaherty, WIRED, 31 Dec. 2023 The flaw is the third zero-day exploit Google has uncovered this year targeting Chrome users. —

Michael Kan, PCMAG, 6 June 2023 Getty Images On Monday, Cisco reported that a critical zero-day vulnerability in devices running IOS XE software was being exploited by an unknown threat actor who was using it to backdoor vulnerable networks. —

Dan Goodin, Ars Technica, 17 Oct. 2023

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'zero-day.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.