Thwarting Stack-Frame Analysis

Created the Monday 13 June 2022. Updated 9 months, 3 weeks ago.

Thwarting Stack-Frame Analysis is a technique used by malware to make it more difficult for security analysts to reverse engineer and analyze the code. A stack frame is a collection of data associated with a function, including local variables, arguments passed to the function, and the return address. Disassemblers can use information from the stack frame to understand a function's behavior.

However, malware authors can use various techniques to defeat this analysis and make it harder to understand the code. For example, they may use complex control flow structures, such as nested loops and conditionals, to make it difficult for the disassembler to track the flow of execution.

They may also use techniques like code obfuscation and API hashing to hide the names of functions and make it harder to identify potentially malicious behavior. By using these techniques, malware authors can make it more difficult for security analysts to analyze and understand their code, and thwart stack-frame analysis.

Technique Identifier

U0219

Technique Tags

Stack frame Disassembly Control flow

Featured Windows API's

Below, you will find a list of the most commonly used Windows API's that are currently utilized by malware authors for current evasion technique. This list is meant to provide an overview of the API's that are commonly used for this purpose. If there are any API's that you feel should be included on this list, please do not hesitate to contact us. We will be happy to update the list and provide any additional information or documentation that may be helpful.

Code Snippets

Description

In this code, the thwart_stack_frame function uses complex control flow structures and API hashing to make it more difficult for a disassembler to analyze the code and understand its behavior. By using these techniques, malware authors can thwart stack-frame analysis and make it harder for security analysts to reverse engineer and understand their code.

#include <stdio.h>
#include <Windows.h>

// Function to obfuscate the names of APIs
unsigned long hash(const char *str)
{
    unsigned long hash = 5381;
    int c;

    while (c = *str++)
        hash = ((hash << 5) + hash) + c; /* hash * 33 + c */

    return hash;
}

// Function to thwart stack-frame analysis
void thwart_stack_frame()
{
    // Use complex control flow structures to make it
    // difficult for the disassembler to track the flow
    // of execution
    int i, j, k;
    for (i = 0; i < 10; i++)
    {
        if (i % 2 == 0)
        {
            for (j = 0; j < 10; j++)
            {
                if (j % 2 == 1)
                {
                    for (k = 0; k < 10; k++)
                    {
                        if (k % 2 == 0)
                        {
                            // Use API hashing to hide the names
                            // of the APIs we want to call
                            HMODULE hKernel32 = LoadLibrary((LPCSTR) hash("kernel32.dll"));
                            LPVOID lpExitProcess = GetProcAddress(hKernel32, (LPCSTR) hash("ExitProcess"));

                            // Call the ExitProcess API
                            ((void (WINAPI *)(UINT))lpExitProcess)(0);

                            // Clean up
                            FreeLibrary(hKernel32);
                        }
                    }
                }
            }
        }
    }
}

int main()
{
    thwart_stack_frame();

    return 0;
}

Additional Resources

External Links

The resources provided below are associated links that will give you even more detailed information and research on current evasion technique. It is important to note that, while these resources may be helpful, it is important to exercise caution when following external links. As always, be careful when clicking on links from unknown sources, as they may lead to malicious content.

https://1malware1.medium.com/anti-disassembly-techniques-e012338f2ae0