DSi system flaws
Undefined instruction/abort exception handler backed by RAM not cleared on reset
Much like the 3DS boot0, some of the DSi's exception handlers are backed by RAM which isn't immediately cleared on a reset. Using fault injection, it is possible to cause an undefined instruction exception before the clearing happens, making the CPU jump to code remaining in RAM from the previous boot cycle. This only works on the ARM7, as on the ARM9, it is backed by main memory, which is only initialized by boot1.
Poor System Menu TMD size check
boot1 loads the System Menu's TMD for verification and loading, and it attempts to check the size. However, instead of checking if
size > capacity, it checks if
size > size, which is always false, resulting in a buffer overflow.
Discovered in August 2017 by Nocash
DS games are not patched to verify overlays
While the System Menu checks all cartridge overlays to prevent unauthorized software, no such check exists when the overlays are actually loaded, despite an MIOS-like patcher being possible to implement. By changing the overlay after it is checked, it is possible to run arbitrary code.