Since ROP relies on RET instructions, where the address of the next instruction to execute is fetched from a stack, stack corruption plays a critical role in ROP attacks. CET enables the OS to create a Shadow Stack, which is designed to be protected from application code memory accesses, and stores CPU-stored copies of the return addresses. This helps ensure that even when an attacker is able to modify/corrupt the return addresses in the data stack for the purpose of carrying out a ROP attack, the attacker is not able to modify the Shadow Stack, and the CET state machine in the CPU detects mismatches between the address on the shadow and data stack to help prevent the attack via an exception reported to the OS.