Cybersecurity definition
What is Zero-Day?
By Cyber Tool Stack Editorial TeamUpdated
Definition
A vulnerability that's exploited by attackers before the vendor knows about it or has released a fix, leaving defenders with zero days of advance warning to patch.
Where Zero-Day fits in the security landscape
These beginner lessons use this term while explaining the surrounding security control.
Related cybersecurity terms
CVECommon Vulnerabilities and ExposuresA public catalog that assigns a unique identifier to a specific, publicly known software or hardware vulnerability, so vendors, researchers, and tools can all refer to the same flaw unambiguously.KEVKnown Exploited VulnerabilitiesA catalog, maintained by the U.S. Cybersecurity and Infrastructure Security Agency, of vulnerabilities confirmed to be actively exploited by attackers — a fast, evidence-based way to prioritize patching over relying on severity scores alone.