微信逆向:定位功能调用(以文本消息发送为例)

selph
selph
发布于 2024-07-03 / 447 阅读
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微信逆向:定位功能调用(以文本消息发送为例)

#re

授人以鱼不如授人以渔

定位功能call的方法思路是通用的,这一套流程对定位其他功能也适用

第二篇,以分析文本消息发送call为例,写代码调用实现发文本消息的功能

有什么想看什么主题,可以在评论区回复,随缘更新

环境准备

  • wechat x64版本
  • x64dbg
  • ida 或者 ghidra
  • debugview++
  • Visual Studio 2022

定位发消息 CALL

查看点击发送消息时候出现的日志里有如下几条:

(2024-7-3:10:28:46:698 43868)-i/MainWnd:btn click: sendBtn

(2024-7-3:10:28:46:702 43868)-i/SendMessageMgr:sendTextMsg

(2024-7-3:10:28:46:831 43868)-i/SendMessageMgr:send msg ok. msgId=

log太多了,中间略去了ui相关的,网络相关的log内容,这里有个很可疑的东西出现:SendMessageMgr,这个东西疑似是发消息操作相关的

去字符串里搜索该串:

Address	Length	Type	String
.rdata:0000000184EFAFD0	00000011	C	SendMessageMgr()
.rdata:0000000184EFB0E0	0000001A	C	SendMessageMgr::eventProc
.rdata:0000000184EFB100	0000001F	C	SendMessageMgr::createThumbJpg
.rdata:0000000184EFB138	0000001C	C	SendMessageMgr::sendTextMsg
.rdata:0000000184EFB250	00000020	C	SendMessageMgr::~SendMessageMgr
.rdata:0000000184EFB270	00000012	C	~SendMessageMgr()
.rdata:0000000184EFB290	00000058	C	D:\\Tools\\agent\\workspace\\MicroMsgWindowsV3911\\MicroMsgWin\\02_manager\\SendMessageMgr.cpp
.rdata:0000000184EFB2E8	0000001F	C	SendMessageMgr::SendMessageMgr
.rdata:0000000184EFB308	0000000F	C	SendMessageMgr
.rdata:0000000184EFB7B8	0000001B	C	SendMessageMgr::trySendMP4
.rdata:0000000184EFB840	0000002C	C	SendMessageMgr::removeVideoHeaderAndMoovSwp
.rdata:0000000184EFB930	0000001D	C	SendMessageMgr::sendImageMsg
.rdata:0000000184EFB968	00000023	C	SendMessageMgr::createSendThumbJpg
.rdata:0000000184EFB990	00000023	C	SendMessageMgr::creatSendMiddleJpg
.rdata:0000000184EFBC20	0000002A	C	SendMessageMgr::processCompressedVideoMsg
.rdata:0000000184EFBC68	00000031	C	SendMessageMgr::tryDealWithOtherCompressVideoMsg
.rdata:0000000184EFBCD8	0000001E	C	SendMessageMgr::forwardEmjMsg
.rdata:0000000184EFBD18	00000020	C	SendMessageMgr::forwardVideoMsg
.rdata:0000000184EFBD88	00000021	C	SendMessageMgr::OnSendVideoAdded
.rdata:0000000184EFBEA0	00000026	C	SendMessageMgr::startTransVideoThread
.rdata:0000000184EFBF10	0000001F	C	SendMessageMgr::OnSendImgAdded
.rdata:0000000184EFBF60	00000018	C	SendMessageMgr::sendMsg
.rdata:0000000184EFBF78	0000001B	C	SendMessageMgr::forwordMsg
.data:00000001857B2910	00000029	C	.?AV?$DynamicHandler@VSendMessageMgr@@@@
.data:00000001857B2998	00000015	C	.?AVSendMessageMgr@@
.data:00000001857B29C0	0000002D	C	.?AV?$mmAccountSingleton@VSendMessageMgr@@@@

这里应该是多种发送消息的地方:

  • SendMessageMgr::sendTextMsg
  • SendMessageMgr::trySendMP4
  • SendMessageMgr::sendImageMsg
  • SendMessageMgr::sendMsg

当前的重点是找到文本消息发送的调用,重点去看SendMessageMgr::sendTextMsg,但是发现交叉引用没有,另一个疑似发送文本消息的是SendMessageMgr::sendMsg,这个有交叉引用:

      log_message(
        2,
        (__int64)"D:\\Tools\\agent\\workspace\\MicroMsgWindowsV3911\\MicroMsgWin\\02_manager\\SendMessageMgr.cpp",
        2208,
        (__int64)"SendMessageMgr::sendMsg",
        "SendMessageMgr",
        "xml parse msg failed",
        (__int128 *)v74,
        (__int128 *)Block,
        (__int128 *)v94,
        (__int128 *)v92,
        &v120,
        &v91);

这里有个信息是xml parse msg failed,应该是解析xml格式的内容,同函数内上下浏览,发现还有个字符串:

    v22 = sub_182617210(
            Block,
            L"<msgsource><sec_msg_node><alnode><fr>%d</fr></alnode></sec_msg_node></msgsource>",
            1i64);

应该是拼接xml格式的函数吧?

这里猜测当前的函数就算发送消息的函数,这个xml应该是发送消息时候组装的数据结构

x64dbg 下断这个函数,发送消息试试:

成功断下,rdx是发送目标的wxid,r8是消息内容

经测试,当从调试器里修改消息内容,就会发送被修改过的消息内容,当从调试器里修改wxid,就会发送给修改过的wxid,是这个call没错了

分析发消息 CALL 参数

向上找一层瞅一眼调用时候的参数:

            SendMessageMgr::sendMsg((__int64)v189, (__int64)&Block, v12 + 8, v12 + 80, 1, 1, *(_DWORD *)(v12 + 4), 0i64);
            sub_181B50D80(v189);

在发消息函数下断查看8个参数分别是什么:

  • a1:应该是个类的对象
  • a2:目标wxid指针,wchar_t类型
  • a3:目标消息指针,wchar_t类型
  • a4:指向0的指针,疑似缓冲区
  • a5:1
  • a6:1
  • a7:0
  • a8:0

v12变量应该也是个对象或者结构体,然后参数取值其中的内容

下面的函数紧接着的这个函数也用了v189变量,进去瞅一眼:

void __fastcall sub_181B50D80(char *a1)
{
  void *v2; // rcx
  void *v3; // rcx
  void *v4; // rcx
  void *v5; // rcx
  void *v6; // rcx
  void *v7; // rcx
  void *v8; // rcx
  void *v9; // rcx
  void *v10; // rcx
  void *v11; // rcx
  void *v12; // rcx
  void *v13; // rcx
  void *v14; // rcx
  void *v15; // rcx
  void *v16; // rcx
  void *v17; // rcx
  void *v18; // rcx
  void *v19; // rcx
  void *v20; // rcx
  void *v21; // rcx
  void *v22; // rcx

  *(_QWORD *)a1 = &ChatMsg::`vftable';
  sub_181B51B90(a1 + 1080, a1 + 1080, *(_QWORD *)(*((_QWORD *)a1 + 135) + 8i64));
  j_j_free_1_0(*((void **)a1 + 135));
  sub_181B51510(a1 + 448);
  v2 = (void *)*((_QWORD *)a1 + 50);
  if ( v2 )
  {
    free(v2);
    *((_QWORD *)a1 + 50) = 0i64;
  }
  *((_QWORD *)a1 + 51) = 0i64;
  v3 = (void *)*((_QWORD *)a1 + 52);
  if ( v3 )
  {
    free(v3);
    *((_QWORD *)a1 + 52) = 0i64;
    *((_DWORD *)a1 + 106) = 0;
  }
  v4 = (void *)*((_QWORD *)a1 + 46);
  if ( v4 )
  {
    free(v4);
    *((_QWORD *)a1 + 46) = 0i64;

这应该是个析构函数,疑似ChatMsg相关类的析构,里面是取虚表之后,对各种字段进行释放

对这个虚表查看交叉引用查看到疑似构造函数:

__int64 __fastcall sub_181B59670(__int64 a1)
{
  void *v2; // rcx
  void *v3; // rcx
  _QWORD *v4; // rax

  *(_QWORD *)a1 = &InstanceCounter<ChatMsg,1000>::`vftable';
  sub_181B59010();
  *(_QWORD *)a1 = &ChatMsg::`vftable';
  *(_QWORD *)(a1 + 32) = 0i64;
  *(_DWORD *)(a1 + 40) = 0;
  *(_QWORD *)(a1 + 48) = 0i64;
  *(_QWORD *)(a1 + 56) = 0i64;
  *(_QWORD *)(a1 + 64) = 0i64;
  *(_QWORD *)(a1 + 72) = 0i64;
  *(_QWORD *)(a1 + 80) = 0i64;
  *(_QWORD *)(a1 + 88) = 0i64;
  *(_DWORD *)(a1 + 96) = 0;
  *(_QWORD *)(a1 + 104) = 0i64;
  *(_QWORD *)(a1 + 112) = 0i64;
  *(_QWORD *)(a1 + 120) = 0i64;
  *(_DWORD *)(a1 + 128) = 0;
  v2 = *(void **)(a1 + 104);
  if ( v2 )
  {
    free(v2);
    *(_QWORD *)(a1 + 104) = 0i64;
  }
  *(_QWORD *)(a1 + 112) = 0i64;
  v3 = *(void **)(a1 + 120);
  if ( v3 )
  {
    free(v3);
    *(_QWORD *)(a1 + 120) = 0i64;
    *(_DWORD *)(a1 + 128) = 0;
  }
  *(_QWORD *)(a1 + 136) = 0i64;
  *(_QWORD *)(a1 + 144) = 0i64;
  *(_QWORD *)(a1 + 152) = 0i64;
  *(_DWORD *)(a1 + 160) = 0;
  *(_QWORD *)(a1 + 168) = 0i64;
  *(_DWORD *)(a1 + 176) = 0;
  *(_QWORD *)(a1 + 184) = 0i64;
  *(_DWORD *)(a1 + 192) = 0;
  *(_QWORD *)(a1 + 200) = 0i64;
  *(_DWORD *)(a1 + 208) = 0;
  *(_QWORD *)(a1 + 216) = 0i64;
  *(_QWORD *)(a1 + 224) = 0i64;
  *(_QWORD *)(a1 + 232) = 0i64;
  *(_DWORD *)(a1 + 240) = 0;
  *(_QWORD *)(a1 + 248) = 0i64;
  *(_QWORD *)(a1 + 256) = 0i64;
  *(_QWORD *)(a1 + 264) = 0i64;
  *(_DWORD *)(a1 + 272) = 0;
  *(_QWORD *)(a1 + 280) = 0i64;
  *(_QWORD *)(a1 + 288) = 0i64;
  *(_QWORD *)(a1 + 296) = 0i64;
  *(_DWORD *)(a1 + 304) = 0;
  *(_QWORD *)(a1 + 320) = 0i64;
  *(_QWORD *)(a1 + 328) = 0i64;
  *(_QWORD *)(a1 + 336) = 0i64;
  *(_DWORD *)(a1 + 344) = 0;
  *(_BYTE *)(a1 + 352) = 0;
  *(_DWORD *)(a1 + 356) = 0;
  *(_BYTE *)(a1 + 360) = 0;
  *(_QWORD *)(a1 + 368) = 0i64;
  *(_QWORD *)(a1 + 376) = 0i64;
  *(_QWORD *)(a1 + 384) = 0i64;
  *(_DWORD *)(a1 + 392) = 0;
  *(_QWORD *)(a1 + 400) = 0i64;
  *(_QWORD *)(a1 + 408) = 0i64;
  *(_QWORD *)(a1 + 416) = 0i64;
  *(_DWORD *)(a1 + 424) = 0;
  *(_QWORD *)(a1 + 432) = 0i64;
  *(_QWORD *)(a1 + 440) = 0i64;
  sub_181B59470(a1 + 448);
  *(_DWORD *)(a1 + 1040) = 255;
  *(_BYTE *)(a1 + 1044) = 0;
  *(_DWORD *)(a1 + 1048) = 0;
  *(_BYTE *)(a1 + 1052) = 0;
  *(_QWORD *)(a1 + 1064) = 0i64;
  *(_QWORD *)(a1 + 0x438) = 0i64;
  *(_QWORD *)(a1 + 0x440) = 0i64;
  v4 = operator new(0x70ui64);
  *v4 = v4;
  v4[1] = v4;
  v4[2] = v4;
  *((_WORD *)v4 + 12) = 257;
  *(_QWORD *)(a1 + 0x438) = v4;
  *(_QWORD *)(a1 + 0x448) = 0i64;
  *(_QWORD *)(a1 + 8) = 0i64;
  *(_QWORD *)(a1 + 24) = 0i64;
  *(_QWORD *)(a1 + 16) = 0i64;
  *(_QWORD *)(a1 + 0x420) = 0i64;
  *(_BYTE *)(a1 + 0x430) = 0;
  *(_BYTE *)(a1 + 312) = 0;
  return a1;
}

假如这是真的构造函数,说明这个类的大小是0x450字节,sendmsg这里是第一次用到这个变量,说明这里传入一个大小0x450的缓冲区即可,然后调用完sendmsg再调用下面的析构去释放了,填充行为会在sendmsg里面进行:

  sub_181B70FD0(a1, v121);
  if ( v23 )
    free(v23);
  if ( v25 )
    free(v25);
  sub_181B50D80(v121);
  return a1;

内容:

__int64 __fastcall sub_181B70FD0(__int64 a1, __int64 a2)
{
  *(_QWORD *)a1 = &InstanceCounter<ChatMsg,1000>::`vftable';
  sub_181B59010();
  *(_QWORD *)a1 = &ChatMsg::`vftable';
  *(_QWORD *)(a1 + 8) = *(_QWORD *)(a2 + 8);
  *(_DWORD *)(a1 + 16) = *(_DWORD *)(a2 + 16);
  *(_DWORD *)(a1 + 20) = *(_DWORD *)(a2 + 20);
  *(_QWORD *)(a1 + 24) = *(_QWORD *)(a2 + 24);
  *(_QWORD *)(a1 + 32) = *(_QWORD *)(a2 + 32);
  *(_DWORD *)(a1 + 40) = *(_DWORD *)(a2 + 40);
  *(_QWORD *)(a1 + 48) = *(_QWORD *)(a2 + 48);
  *(_DWORD *)(a1 + 56) = *(_DWORD *)(a2 + 56);
  *(_DWORD *)(a1 + 60) = *(_DWORD *)(a2 + 60);
  *(_DWORD *)(a1 + 64) = *(_DWORD *)(a2 + 64);
  *(_DWORD *)(a1 + 68) = *(_DWORD *)(a2 + 68);
  sub_182615020((void *)(a1 + 72), (void *)(a2 + 72));
  sub_182615020((void *)(a1 + 104), (void *)(a2 + 104));
  sub_182615020((void *)(a1 + 136), (void *)(a2 + 136));
  sub_18260DBF0(a1 + 168, a2 + 168);
  sub_18260DBF0(a1 + 184, a2 + 184);
  sub_18260DBF0(a1 + 200, a2 + 200);
  sub_182615020((void *)(a1 + 216), (void *)(a2 + 216));
  sub_182615020((void *)(a1 + 248), (void *)(a2 + 248));
  sub_182615020((void *)(a1 + 280), (void *)(a2 + 280));
  *(_BYTE *)(a1 + 312) = *(_BYTE *)(a2 + 312);
  sub_182615020((void *)(a1 + 320), (void *)(a2 + 320));
  *(_BYTE *)(a1 + 352) = *(_BYTE *)(a2 + 352);
  *(_DWORD *)(a1 + 356) = *(_DWORD *)(a2 + 356);
  *(_BYTE *)(a1 + 360) = *(_BYTE *)(a2 + 360);
  sub_182615020((void *)(a1 + 368), (void *)(a2 + 368));
  sub_182615020((void *)(a1 + 400), (void *)(a2 + 400));
  *(_DWORD *)(a1 + 432) = *(_DWORD *)(a2 + 432);
  *(_DWORD *)(a1 + 436) = *(_DWORD *)(a2 + 436);
  *(_DWORD *)(a1 + 440) = *(_DWORD *)(a2 + 440);
  *(_DWORD *)(a1 + 444) = *(_DWORD *)(a2 + 444);
  sub_181B71240(a1 + 448, a2 + 448);
  *(_DWORD *)(a1 + 1040) = *(_DWORD *)(a2 + 1040);
  *(_BYTE *)(a1 + 1044) = *(_BYTE *)(a2 + 1044);
  *(_DWORD *)(a1 + 1048) = *(_DWORD *)(a2 + 1048);
  *(_BYTE *)(a1 + 1052) = *(_BYTE *)(a2 + 1052);
  *(_QWORD *)(a1 + 1056) = *(_QWORD *)(a2 + 1056);
  *(_QWORD *)(a1 + 1064) = *(_QWORD *)(a2 + 1064);
  *(_BYTE *)(a1 + 1072) = *(_BYTE *)(a2 + 1072);
  sub_181B728E0(a1 + 1080, a2 + 1080);
  *(_DWORD *)(a1 + 1096) = *(_DWORD *)(a2 + 1096);
  *(_DWORD *)(a1 + 1100) = *(_DWORD *)(a2 + 1100);
  return a1;
}

猜测没错,应该是这样了

那么接下来的问题就是v12是什么?

网上找,发现v12赋值的地方:v12 = *a2

  if ( *(int *)(a1 + 56) <= 0 && *(int *)(a3 + 8) <= 0 || (v11 = a2[1], v12 = *a2, (v13 = (v11 - *a2) / 104) == 0) )

v12来自参数a2的第一个成员,返回上一层查看这个参数来自一个复杂的函数调用,于是就先不管了,直接用硬编码调用试试看

现在的参数:

  • a1:缓冲区:0x450 字节
  • a2:目标wxid指针,wchar_t类型
  • a3:目标消息指针,wchar_t类型
  • a4:缓冲区:大小未知
  • a5:1
  • a6:1
  • a7:0
  • a8:0

代码实现(核心)

实现调用微信的call完成发消息

这里主要就是找到call以及分析参数,找好参数构造好直接调用就行

注意一点就是,这里用的字符串都是结构体,第一个成员是wchar_t指针,第二个成员是长度

struct message {
    wchar_t* msg;
    int len;
};

typedef INT64(__fastcall* _sendMsg)(
    char* a1,
    message* target_wxid,
    message* message,
    char* buffer,
    int a5,
    int a6,
    int a7,
    INT64 a8);

typedef void(__fastcall* _ChatMsg_destruct)(char* a1);

_sendMsg fsendMsg;
_ChatMsg_destruct fChatMsg_destruct;

void sendMsg() {
    HMODULE hMod = GetModuleHandleA("WeChatWin.dll");
    fsendMsg = (_sendMsg)((unsigned long long)hMod + FUNCTION_SendMsg);
    fChatMsg_destruct = (_ChatMsg_destruct)((unsigned long long)hMod + FUNCTION_ChatMsg_Destructor);
  
    char* a1 = (char*)calloc(1,0x450);
    wchar_t* str = L"filehelper";
    wchar_t* str2 = L"start";
    message a2,a3;
    a2.msg = str;
    a2.len = wcslen(str);
    a3.msg = str2;
    a3.len = wcslen(str2);
    char* a4 = (char*)calloc(1,0x450);
    fsendMsg(a1, &a2, &a3, a4, 1, 1, 0, 0);
    fChatMsg_destruct(a1);
	free(a1);
}

实现效果

成功把start发送给文件助手: image

参考资料


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