Security
Zero-day
In short and in plain language
A zero-day is a security gap that has no fix yet.
The gap is already known or already being used. But the vendor has not yet been able to fix it.
Until a patch comes out, often only stopgap steps can lower the risk.
For operators, it matters to hear about such reports quickly and judge them.
Definition
A zero-day is a security gap that is exploited or known before the vendor could provide a fix. Until a patch appears, often only interim measures can reduce the risk. For operators it matters to learn about such reports quickly and to assess them.