Zero-day
Also called 0-day, zero-day vulnerability, zero-day exploit
A security flaw that attackers know about before the maker has a fix, so defenders have had zero days to patch it.
Software has flaws nobody has found yet. When an attacker finds one first and uses it, the maker has had no time to write a fix and you have had no time to install one. That is a zero-day: the "zero" counts the days defenders have had.
Zero-days get the headlines because no patch exists to stop them. Most attackers don't need one. The AI-assisted intrusions examined in detail so far came through ordinary doors, and none depended on a technique defenders hadn't seen.
AI is changing the cost of finding them. Models can read code and firmware for weaknesses much faster than a person can, and one attacker was seen pointing agents at network appliances in a loop. Defenders can run the same search on their own code.
For example
A flaw in a firewall is being used to break into companies, and the vendor only learns of it from the first victims.
Put it to use
Where you'll meet zero-day in ChatGPT, Gemini and Claude, how to use it there, and the mix-up most people make.
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