can you telnet into the system ?
if you can , then you can use dd command to dumping the NAND .
just
dd if=/dev/mtd0 of=/media/usb/mtd0.bin bs=128k
dd if=/dev/mtd1 of=/media/usb/mtd1.bin bs=128k
don't forget to replace /media/usb to your real device mount name.
maybe /media/usb ot /mnt/usb