CIS Security has published an excellent list of older software versions where vendors no longer provide support (as of  October 2019)

End-of-Support Software Report List

https://www.cisecurity.org/wp-content/uploads/2019/10/EOS-Report-October.pdf

Using unsupported software and firmware/hardware, puts organizations at risk:
1. Subsequent vulnerability disclosures place your organization at significant risk.
2. Subject your organization to regulatory compliance issues/violations.
3. Increases support costs by having a need for extended support.