What are 'zero-day vulnerabilities'?

Zero-day vulnerabilities refer to security flaws in software that are discovered and exploited by attackers before the vendor or developers are aware of them. The term "zero-day" signifies that the developers have zero days to fix the vulnerability because they do not even know it exists. This makes zero-day vulnerabilities particularly dangerous, as there is often no patch or fix available at the time of the exploit, leaving users and systems vulnerable to attacks.

In contrast, flaws discovered after software is released may not necessarily be zero-day vulnerabilities since they can be addressed through updates and patches once identified. Security flaws that are publicly exposed can become known vulnerabilities, as they can be fixed once a vendor acknowledges and acts upon them. Similarly, design errors in programming refer to issues that may exist in the architecture of software but do not align directly with the concept of undiscovered weaknesses that attackers can exploit before any notice is taken by the software developers. Therefore, the correct understanding of zero-day vulnerabilities hinges on the lack of awareness from the software vendor at the moment the exploit is taking place.