Zero day

A zero day is a security vulnerability that is unknown to the software or hardware vendor and has not yet been patched.

A zero day is a security vulnerability unknown to the vendor with no patch available. The term also covers the exploit or attack that uses such a flaw before defenders can fix it.

What it is

In cybersecurity, a zero-day vulnerability is a flaw in software, hardware, or firmware that the vendor hasn't discovered or patched yet. A zero-day exploit is the code or method used to take advantage of that flaw, and a zero-day attack is when that exploit is deployed before any fix exists.

Why it matters

Zero-day flaws are high-risk because they can enable unauthorized access, malware delivery, or data theft without detection by standard signature-based defences. Since defenders have had zero days to prepare, these vulnerabilities can be exploited quietly until discovered and mitigated.

Key details

Defence relies on behaviour-based detection, network monitoring, and layered controls rather than signatures alone. Rapid patching once fixes are released is critical. In Canada, zero-day threats are treated as high-priority for individuals, businesses, and government systems.