Recently, some network devices caught my attention both on Aliexpress and Alibaba. Specifically, I found some interesting outdoor equipment for a very low price, ranging between 10-25$.
These are 2.4ghz AR9330 based boards, powered via POE (although on a non standard voltage), with two 10/100/1000 ethernet ports, an integrated antenna and a waterproof enclosure.
I received the first one from Aliexpress but i plan to get some other to test as well.
From the PCB picture it is clear that the board has an easily accessible serial header and that it has a SOIC8 flash chip (Winbond 25Q64). Given this info, there are two possibilities to start learning about the board via hardware: connecting to the serial console and get whatever the oem firmware prints out and do a direct hardware image of the flash chip.
Before even trying the SOIC clip or the serial port i wanted to check around the stock firmware. It looks like the device has no DHCP server but it has a fixed `192.168.0.1` ip address and default `admin:admin` credentials.
By default, there's only the web intrace and a telnet server listening on the public interface. The credentials for the telnet interface are `root` without password.
While upon collecting the user is dropped in a restriced pompt with few commands available, it is possible to inject commands in almost any of it via common shell separators `|;&`.
With the command injection is easy to understand that the device is already running a heavily customized OpenWRT fork, running on `Linux 2.6.31`.
By knowing the size of each mtd partition, we get to know that it has a 8M flash chip. This makes sense given that the chip has written on it `25Q64`, where `64` is the size in Megabits.
Using `dd` it is possible to dump each partition, download it and even reasseble the full firmware image simply with `cat` afterwards.
-rwxrwxrwx 1 user user 8388608 Apr 12 12:40 flash.bin
```
Where `8388608/1024=8192K`.
When the device boots up, a lot of custom scripts and services will run. The most custom part of the firmware, which means the web interface and their custom binaries are somehow encrypted or more simply obfuscated and loaded at runtime in ram. At rest, the obfuscated files are called `/usr/web.bin`, `/usr/sbin.bin`, `/usr/apps.bin`. The executable responsabile for decrypting them to more simpler `tgz` archives is called `ap_monitor`. Ghidra sucessfully decompile this binary and the obfuscation mechanism is not very complicated and could reversed with not too much effort but there's proably no reason to do so.
Since I was unable to find the manufacturer both on the package or anywhere else, i'll refer to it as `ZiKing` as it seems that's the name stated in their own proprietary config file. On Aliexpress, the same device is also often said to be made by `ANDDEAR`. Both do not seem to have any presence on the English internet.
The only thing actually existing, given that as of now the website shows a default page, is [their IANA assignment number](https://oidref.com/1.3.6.1.4.1.37260).
Check that all the checksums do match. In case they don't there's probably something wrong in the clip position or in the wiring. Remember that no pin should left floating even if it's not useful for the operation. /WP and /HOLD should be always connected to something like GND or VCC.
The serial header is easy to work with and has clearly written the pinout on it. Any cheap usb adapter will probably work. In my case the baudrate is 115200, however, a script like [baudare.py](https://github.com/somu1795/baudrate) should do the trick.
Common softwares for serial communication are `minicom` and `screen`.
The info learnet from `proc/mtd` are extremely useful.
*`mtd0 u-boot` is a 64K partition which contains the u-boot bootloader
*`mtd1 u-boot-env` is a 64K partition containing the u-boot configuration
*`mtd2 rootfs` is a jffs2 partition containing the actual image
*`mtd3 uImage` is a squashfs kernel image
*`mtd4 rootfs1` is a jffs2 partition containing a secondary image, probably used for recovery
*`mtd5 NVRAM` is a 64K partition which contains a `tgz` for OEM system configuration files
*`mtd6 ART` is a 64K partition [that contains calibration data for the radio chip](https://github.com/pepe2k/ar9300_eeprom)
The total size is of course 8192K. The partitions are not partitions in an EXT or NTFS sense. The data is just contiguos on the flash but the bootloader and the kernel are responsible for considering the different regions separate.
That's the reason because `cat` works and it is so simple to work with them.
Since for vanilla OpenWRT a custom partition for configuration is not needed, and two rootfs aren't useful and everything can be packed in a single partition with more space for packages and user data our target could be:
*`mtd0 u-boot` oeiginal image
*`mtd1 u-boot-env` some values here needs to be modified
*`mtd2 firmware` 8000K OpenWRT partition (`firmware` is the standard OpenWRT naming)
*`mtd3 ART` original image
On some other devices this is not needed because maybe the partition layotu already makes sense: ie there are no duplicate rootfs data. They are a bit easier to play with because in that case there's probably no need to manipulate the boot environment. Furthermore, building an image for flashing trough the OEM web interface might be not possible.
### U-Boot
U-boot is an Open Source Bootloader mainly for embedded devices. While it is actively developed, the actual version depends on the SDK a vendor provides for its SoC.
Atheros, for `ar9330` seems to have used 1.4 as base, which is almost a decade old.
