Do I need CCNA for a security career or is it a detour?

You need the networking, not necessarily the cert. Subnetting, how TCP/IP actually flows, what a switch/router/firewall do, VLANs, NAT — you'll use these daily and they're CCNA's first half. If you learn best with a goal, get the cert; if not, the fundamentals alone are the real requirement.

I did the first half of CCNA content and stopped at the cert line — no regrets, the fundamentals carried over.