An issue was discovered on Renesas SmartBond DA14691, DA14695, DA14697, and DA14699 devices. The Nonce used for on-the-fly decryption of flash images is stored in an unsigned header, allowing its value to be modified without invalidating the signature used for secureboot image verification. Because the encryption engine for on-the-fly decryption uses AES in CTR mode without authentication, an attacker-modified Nonce can result in execution of arbitrary code.