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See also: zero day


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zero-day (not comparable)

  1. (computing, idiomatic) (of vulnerability) newly discovered, and therefore still not fixed and possibly exploited by hackers or other criminals
  2. (computing, idiomatic) (of exploit, its threat, or attack) benefiting from newly found and yet unpatched or unmitigated flaw in software or hardware; using zero-day vulnerability
    • 2003, John Viega, Matt Messier, Secure Programming Cookbook for C and C++
      If your software is popular and has a high demand, you will want to defend against the "zero-day" cracker.
    • 2014, Michael Gregg, CASP CompTIA Advanced Security Practitioner Study Guide: Exam CAS-002[1]:
      Before discussing ways to counter zero-day attacks, let's begin with the definition of what a zero-day attack is. A zero-day attack is one that the vendor does not yet know about or hasn't been fixed.
    • 2005, Valdes et al, Recent Advances in Intrusion Detection
      Automatically creating reliable signatures of zero-day exploits is the focus of intense research efforts.
  3. Used other than figuratively or idiomatically: see zero,‎ day.
    Average residues of 1.44 and 2.18 mg/kg chlortetracycline were seen in liver and kidney, respectively, at zero-day withdrawal.


zero-day (plural zero-days)

  1. (computing, idiomatic) vulnerability that has been discovered recently, and is yet unpatched or unmitigated; zero-day vulnerability
    New Internet Explorer zero-day exploited in Hong Kong attacks
    These days, however, more zero days are being used and discovered.
    All the four zero-days originally were reported to Microsoft, affecting Internet Explorer on the desktop.