Buffer overflow in bech32_decode/cash_decode

The C reference implementation for bech32 has an unsigned integer overflow that can lead to a buffer overflow. The bug was fixed by preventing the out-of-bounds accesses in the code. Later, gabriel Campana reported the same issue in cash_decode function, which was fixed in the same firmware update.

Fixed in firmware 1.7.1 by commits 5c6b472 and 2bbbc3e.

Read more at Christian's blog or ours.