The user information configuration registers (UICR) and factory information configuration registers (FICR) are always considered as secure. FICR registers are read-only. UICR registers can be read and written by secure code only.
Writing new values to user information configuration registers must follow the procedure described in NVMC — Non-volatile memory controller. Code execution from FICR and UICR address spaces will always be reported as an access violation except during a debug session.