Improper Access Control in kctf

kCTF is a Kubernetes-based infrastructure for capture the flag (CTF) competitions. Prior to version 1.6.0, the kctf cluster set-src-ip-ranges was broken and allowed traffic from any IP. The problem has been patched in v1.6.0. As a workaround, those who want to test challenges privately can mark them as `public: false` and use `kctf chal debug port-forward` to connect.