It would have to be in the presence of UV light surely... free radical substitution? I don't know if this is possible or not, as cyclohexane is very inert. Only really reacts with Superacids like Fluoroantimonic Acid.
If substitution can occur, which I doubt, then:
C6H12 + Cl2 -> C6H11Cl + HCl
Further substitution would occur, leading to C6H6C6 eventually:
C6H12 + 6Cl2 -> C6H6Cl6 + 6HCl
Same reactions with Br2 and I2.
I can repost with initiation, propogation and termination if you like. But bear in mind that this would only occur in quite harsh conditions (eg very hot, high intensity UV light)...