Using file command we can get some information from the firmware binary files:
Let's using binwalk - our best friend
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:
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
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: