On Xilinx Zynq-7000 SoC devices physical modification of an SD boot image allows for a buffer overflow attack in the ROM. Because the Zynq-7000's boot image header is unencrypted and unauthenticated before use an attacker can modify the boot header stored on an SD card so that a secure image appears to be unencrypted and they will be able to modify the full range of register initialization values. Normally these registers will be restricted when booting securely. Of importance to this attack are two registers that control the SD card's transfer type and transfer size. These registers could be modified a way that causes a buffer overflow in the ROM.