Advanced – Security Testing
Zero-Day – ISTQB Definition
Last Updated: July 12, 2026 · SoftwareTestPilot QA Team
Official ISTQB Definition
A software vulnerability that is unknown to those who should be interested in mitigating it, including the vendor.
In simple words
A brand-new vulnerability with no patch available yet.
Exam tip
Zero-days are the reason defence-in-depth matters — patching alone is not enough.
Related terms
Practice this term in the ISTQB Mock Test
40 CTFL v4.0 questions, 60-minute timer, instant scoring and chapter-wise breakdown.
Practice in Mock Test