Unpatchable BootROM Flaw Impacts Apple A12, A13 Chips

**Executive summary:** Researchers discovered a BootROM-level vulnerability named usbliter8 that leverages a Synopsys DesignWare USB controller DMA underflow plus SecureROM configuration flaws to achieve persistent boot-chain compromise on Apple A12, S4/S5 and A13 devices; exploitation requires DFU mode and custom RP2350 microcontroller hardware, cannot be fully remediated via software updates, and is mitigated in newer chips (A14+) that configure DART correctly.