In them it is possible to find signatures of formats or algorithms used to generate them. This is a clear example of taking entropy as an accurate measure of randomness is a mistake.
Presence of the string “Authentication successful” indicates that this function will be called if the password was correct. Ghidra will prompt to analyze the file and we click yes keeping the default analysis options. Let’s have a look at the disassembled code after analysis finishes. To upload the binary, navigate to the ESPEasy web interface and enter the “Tools ” section.
The researcher must consult the documentation of the tool used to be sure to perform a conversion to binary format. Hence our next step is to find the correct loading address in memory for a STM32 firmware. This information can often be found in the device datasheet and in compiler header files. Again, a start code is defined along with different fields to describe data records in hexadecimal format. It can be distinguished because in this case the start code is an ‘S’. To convert this format to binary, the same tools can be used as in the previous section.
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- As soon as the flashing process starts, the tool will display two MAC Addresses as AP and STA.
- Running them without parameters
- A complete executable is composed of many different sections, and the linker script is what describes where they should go and how to refer to them.
A study of the entropy across a firmware image, therefore, can reveal encrypted or compressed sections. Before trying to identify the sections with file systems, to understand their contents, it is useful to identify the format of the firmware image.
As we have seen, analyzing and extracting the filesystem is a fundamental phase in the analysis of the firmware of a device. One of the steps that can be carried out when conducting an IoT security audit. Depending on the type of file system found in Stock Firmware the firmware, different tools will be required to extracting the filesystem. In addition, for certain file systems and compression formats, non-standard signatures may be encountered. Many device manufacturers use modified signatures to indicate the format.