Integer underflow of net_buf length in the MCUmgr serial (SMP over console) transport leads to out-of-bounds read
The MCUmgr SMP-over-console transport decodes a base64 frame, reads a 16-bit packet length from it, verifies a CRC and then unconditionally strips the trailing CRC with rx_ctxt->nb->len -= 2U; in mcumgr_serial_process_fr…