Getting in at the "ground floor" of a new datacentre build is pretty much the ultimate exploit. Imagine getting in at the centre of a new Meet-Me room (https://en.wikipedia.org/wiki/Meet-me_room) and having persistent access to key switches there.
Cloudflare datacentres tend to be at the hub of insane amounts of data traffic. The fact that the attacker knew how valuable a "pre-production" data centre is means that cloudflare probably realized themselves that it would be a 100% game over if someone managed to get a foot hold there before the regular security systems are set up. It would be a company ending event if someone managed to install themselves inside a data centre while it was being built/brought up.
Also remember, at the beginning of data centre builds, all switches/equipment have default / blank root passwords (admin/admin), and all switch/equipment firmware are old and full of exploits (you either go into each one and update the firmware one by one or hook them up to automation for fleet wide patching) Imagine that this exploit is taking place before automation services had a chance to patch all the firmware ... that's a "return all devices to make sure the manufacturer ships us something new" event.
Getting in at the "ground floor" of a new datacentre build is pretty much the ultimate exploit. Imagine getting in at the centre of a new Meet-Me room (https://en.wikipedia.org/wiki/Meet-me_room) and having persistent access to key switches there.
Cloudflare datacentres tend to be at the hub of insane amounts of data traffic. The fact that the attacker knew how valuable a "pre-production" data centre is means that cloudflare probably realized themselves that it would be a 100% game over if someone managed to get a foot hold there before the regular security systems are set up. It would be a company ending event if someone managed to install themselves inside a data centre while it was being built/brought up.
Also remember, at the beginning of data centre builds, all switches/equipment have default / blank root passwords (admin/admin), and all switch/equipment firmware are old and full of exploits (you either go into each one and update the firmware one by one or hook them up to automation for fleet wide patching) Imagine that this exploit is taking place before automation services had a chance to patch all the firmware ... that's a "return all devices to make sure the manufacturer ships us something new" event.