It is always recommended not to leak the information of network protocol which is running in ISP core. Why it is said, without leaking the information can someone gain the information of any ISP.
Answer is yes.
So in the docment attached I have tested a scenario in which ISP is using OSPF and one of its esteemed client who is attached to any of PE be able to access the ISP network consequence major downtime.
Thats why it is recommended not to use OSPF,EIGRP,IGRP,RIP with customer, If you are using then do it in a very secured manner. One mistake may lead kick you out from the organization.