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
James BamfordThere's a zero-day vulnerability in RealPlayer and Internet Explorer that allows malicious code to be installed …—Mark Hopkins
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
Lev GrossmanExamples of zero-day in a Sentence
Recent Examples on the Web
The zero-day vulnerabilities were found before developers were made aware and could patch them.
—Kate O'Flaherty, Forbes.com, 17 Apr. 2025
The group was also willing to pay premium prices for zero-day exploits from exploit brokers.
—ArsTechnica, 8 Apr. 2025
According to Kaspersky’s report, the malware was based on a zero-day vulnerability, later identified as CVE-2025-2783.
—Kurt Knutsson, Cyberguy Report, FOXNews.com, 1 Apr. 2025
All those users must now update Chrome, after Google warned that a new zero-day exploit has been found in the wild.
—Zak Doffman, Forbes.com, 28 Mar. 2025
See All Example Sentences for zero-day
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Kate O'Flaherty, Forbes.com, 17 Apr. 2025
The group was also willing to pay premium prices for zero-day exploits from exploit brokers.
—ArsTechnica, 8 Apr. 2025
According to Kaspersky’s report, the malware was based on a zero-day vulnerability, later identified as CVE-2025-2783.
—Kurt Knutsson, Cyberguy Report, FOXNews.com, 1 Apr. 2025
All those users must now update Chrome, after Google warned that a new zero-day exploit has been found in the wild.
—Zak Doffman, Forbes.com, 28 Mar. 2025
See All Example Sentences for zero-day
Cite this Entry
“Zero-day.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/zero-day. Accessed 24 Apr. 2025.
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