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• Chapter 1 – Recovering the Passwords

  yaluke • 6 hours ago • 0 comments

  The router had spent the last seven years forgotten in the back of a drawer. During that time, I used a device provided by my internet service provider. After connecting the old router to power, it booted successfully and started serving a network. However, I had no idea what the passwords were—neither for Wi-Fi nor for administration access. Before resorting to pressing the reset button, I decided to experiment and see if I could somehow retrieve the passwords.

  Disassembling the Router

  Disassembly was straightforward, though reading instructions beforehand would have been beneficial—I ended up breaking two fasteners in the process. A quick inspection of the PCB revealed two connectors: one 1x4-pin and one 2x7-pin connector. Documentation found on openwrt.org confirmed these connectors as UART and JTAG interfaces:

  Connecting via UART Using Raspberry Pi 5

  Since I didn't have a USB-to-serial adapter available, I decided to use a Raspberry Pi 5 (RPi) to communicate with the router through UART. The configuration was simple:

  1. First, I enabled the serial hardware interface on the Raspberry Pi using `raspi-config`.
  2. Next, with both devices powered off, I connected them as follows:

  Raspberry Pi 5	Router UART
  GND (pin 6)	pin 2
  GPIO14/UART0 TX (pin 8)	pin 3
  GPIO15/UART0 RX (pin 10)	pin 4

  After making these connections, I powered on only the Raspberry Pi.

  Using minicom to Access Router's Serial Console

  The first tool I used for communication was `minicom`, installed on Raspberry Pi with:

  sudo apt install minicom

  Using communication parameters provided by OpenWrt documentation—baud rate: 115200, data bits: 8, parity: none, stop bits: 1, flow control: none—and the RPi UART device (`/dev/ttyAMA0`), the command line looked like this:

  minicom -b 115200 -8 -D /dev/ttyAMA0

  Minicom then waited for data from the router. Upon powering up the router, after a few seconds I saw this output:

  When seeing "Autobooting in 1 second," I quickly typed `tpl` followed by <enter> to interrupt booting and enter the boot prompt. At this prompt, various commands were available (`help` lists them all). However, only one command seemed useful for inspecting memory contents: `md` (memory display).
  

  Dumping Router Flash Memory

  I assumed passwords were stored somewhere within flash memory, which should be mapped into address space. Based on OpenWrt documentation (flash layout and flashing instructions), I confirmed that flash memory starts at address `0xbf000000` and occupies an 8 MB address range. This was precisely the area I wanted to dump and analyze.

  Minicom offers an option (`-C`) to log all communication into a file. Initially, my idea was to use this feature along with the `md.b` command to dump flash memory:

  Output from `md` can be parsed easily and converted into binary format for an exact copy of flash data. Unfortunately, random chunks of data occasionally went missing during dumping—I wasn't sure if this was due to issues with the router itself, Raspberry Pi hardware limitations, or something else entirely.

  Reliable Data Dumping with Python Script

  To ensure reliable data dumping—checking for missing data and retrying failed reads—I decided to write a Python script using the `pyserial` library (`pip3 install pyserial`). Here's a snippet of Python code that automates connecting to the router's boot prompt (eliminating manual typing of `tpl`):

  import serial
  from time import sleep
  
  with serial.Serial('/dev/ttyAMA0', 115200, timeout=1) as conn:
          # connect and "login"
          logged_in = False
          buffer = ''
          while(not logged_in):
              x = str(conn.read(), encoding='utf-8')
              buffer = buffer + x
              print(x, end='')
              if len(buffer) >= 24 and buffer[-24:] == 'Autobooting in 1 seconds':
                  # now we have 1 second to "login"...
                  sleep(0.1)
                  # by sending 'tpl' string to device
                  conn.write(bytes('tpl\n', 'utf-8'))
                  # let's read all the stuff before sending next command
                  x = str(conn.read(100), encoding='utf-8')
                  print(x)
                  logged_in = True

  ... Read more »

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