At one of our newest customers, I recently stumbled upon a standalone NetScaler still running NSOS 12.1. Please guys, upgrade your 12.1 NetScalers immediately! NSOS 12.1 is well-known to several vulnerabilities and all those black hats and script kiddies are out there, hacking and compromising your 12.1 NetScaler in just a few minutes!
My recommendation: as 13.0 support will end mid 2024, upgrade to the latest 13.1. In case you need new 14.1 features, go ahead with that release then.
Next, in most cases we had to re-issue the NetScaler license files as the license got invalid with the upgrade. So lookup the according MyCitrix credentials. ;- )