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Reverse Trendnet TS-S402 firmware

Start reversing Trendnet TS-S402 firmware device.

Downloading the firmware from the vendor webpage

First, we need to download the firmware from the vendor webpage. I downloaded the 2015 version:
Next, unzip the firmware file:
unzip FW_TS-S402\(2.00.13\).zip

Inspecting the binary files

Using file command we can get some information from the firmware binary files:
file REMOTE_PACKAGE_2_30.bin
file TS-S402_FW_2_00_13.bin
Or not
Let's using binwalk - our best friend
binwalk TS-S402_FW_2_00_13.bin
We can observe a lot of LZMA data, however, we got an interesting gzip compressed file as well. From this point, we can use the -x option to ignore LZMA compression and extract only the gzip file. Something like this:
binwalk -ex lzma TS-S402_FW_2_00_13.bin
-e: extraction option -x: ignore option
Accessing the _TS-S402-FW... folder, we can observe two files:
file 20
20: POSIX tar archive (GNU)
Ok, 20 file is another compressed file. Let's renaming it and unarchiving it.
mv 20 20.tar
tar -xvf 20.tar
Yeah dude, it was a strong journey!

Mount the filesystem

mkdir sqsh
sudo mount rootfs.armeb.squashfs ./sqsh/ -t squash fs -o loop
If you got an error, don't worry about that!
If we look at the hexadecimal, we can see the file format:
cat rootfs.armeb.squashfs | xxd | less
./sasquatch rootfs.armeb.squashfs