넘어간다제~

#include <stdio.h>

#include <stdlib.h>

#include <stdint.h>

 

void execute(int user_input, int length) {

    uint8_t code_buffer[128];

    uint8_t *code_ptr;

    uint32_t buffer_length;

    uint32_t adjusted_length;

    int read_index = 0;

    uint32_t write_index = 0;

 

    if (user_input == 0 || length == 0) {

        exit(1);  // Exit if input is invalid

    }

 

    adjusted_length = length * 2;

    buffer_length = adjusted_length;

 

    // Calculate the required padding for alignment

    uint32_t alignment_padding = (adjusted_length + 16) / 16 * 16 - adjusted_length;

    adjusted_length += alignment_padding;

 

    // Ensure the buffer is within bounds

    if (adjusted_length > sizeof(code_buffer) - 1) {

        exit(1);  // Exit if calculated length exceeds buffer size

    }

 

    while (write_index < buffer_length) {

        // Apply a simple transformation to each byte from user_input based on an index condition

        if ((write_index % 4) < 2) {

            read_index++;

            code_buffer[write_index] = *((uint8_t *)user_input + read_index);

        } else {

            code_buffer[write_index] = 0x90;  // NOP instruction in x86

        }

        write_index++;

    }

 

    // Append a return instruction to the generated code

    code_buffer[buffer_length] = 0xC3;  // RET instruction in x86

 

    // Cast the buffer to a function pointer and execute

    code_ptr = code_buffer;

    ((void (*)(void))code_ptr)();  // Execute the dynamically created function

}

//void filter(char* buffer, int buffer_length, char* newBuffer);

void filter(char* buffer, int buffer_length, char* newBuffer)

{

    int double_length;

    int i;

    int j;

if(buffer!=NULL && buffer_length!=0)

    {

        double_length = buffer_length*2;

        i = 0;

        for(j=0; j<double_length; j++)

        {

            if((j & 3) < 2)

            {

                newBuffer[j] = buffer[i];

                i++;

            }

            else

            {

                newBuffer[j] = 0x81;

            }

        }

        newBuffer[j] = '\0';

    }

}

 

int main(int argc, char** argv)

{

    char shellcode[1000];

    char filtered_shellcode[2000];

    int temp;

    char character;

    int i;

    printf("Insert the shellcode: ");

    temp = fgetc(stdin);

    character = (char)temp;

    i = 0;

    while(character!='\n' && i<999)

    {

        shellcode[i] = character;

        temp = fgetc(stdin);

        character = (char)temp;

        i++;

    }

    shellcode[i] = '\0';

    execute(shellcode, i, filtered_shellcode);

    printf("The filtered shellcode is the following one: %s", filtered_shellcode);

}