What is a zero-day, and can anything detect it?
A zero-day is a vulnerability that attackers exploit before the vendor has released a fix, so patching cannot help yet and no signatures exist. Zero-days are expensive and often used against internet-facing systems such as VPN gateways, firewalls and file-transfer servers. Detection therefore relies on what happens after the exploit: an appliance that suddenly talks to new outside servers, a web server that starts scanning the internal network, new administrator sessions, data leaving. Reduce exposure by keeping as few services as possible reachable from the internet, putting management interfaces behind a VPN, and following vendor advisories and CISA's Known Exploited Vulnerabilities catalogue, so that you patch the moment a fix appears. NetSenX does not detect the exploit itself; it flags the behaviour that follows, such as beaconing, scanning and unusual outbound volume, on every plan.