I was trying to setup an OpenSSH VPN today I and I kept getting the same error (in ssh -v -v)
sys_tun_open: failed to open tunnel control interface: Permission deniedI couldn't for the life of me figure out why. Turns out you have to do PermitTunnel Yes in your sshd config on both the client and the server. I only had that option on the server. If the error message were a little more descriptive I could have saved a lot of troubleshooting time.