Hack the IDLE.DLL of Yahoo Messenger

Yahoo Messenger is very nice IM software. But it used the very old window HOOK functions to detect the user idle time through IDLE.DLL. The idle.dll is a 6k DLL file which created with Microsoft VC 7.1 and linked with MSVCR71.DLL. In this way, the IDLE.DLL will be injected to all the user applications, and hook the message queue of all applications, and it will also injects the MSVCR71.DLL into the user applications. Please refer MSDN for details about the Windows HOOK function.

Yahoo Messenger 是一个很不错的IM软件。但是它是用了一个非常陈旧的Windows Hook功能,因此制造了一个idle.dll 用来来检测用户的发呆时间。这个IDLE.DLL 文件看起来并不大,只有6k,其实它是一个用VC7.1编译产生的动态链接库并且动态链接到MSVCR71.DLL。 由于HOOK函数需要把 IDLE.DLL 注入到所有的用户程序中,MSVCR71.DLL 也会被注入到所有的用户程序中。 而且这个IDLE.DLL 会进入所有用户程序的消息循环。在所有的程序中都有这个 idle.dll 实在是让人不爽。 ;)

Let's check the IDLE.DLL
下面就让我们看看这 IDLE.DLL

C:\Program Files\Yahoo!\Messenger>dumpbin /exports idle.dll
Microsoft (R) COFF/PE Dumper Version 8.00.50727.42
Copyright (C) Microsoft Corporation. All rights reserved.

Dump of file idle.dll

File Type: DLL

Section contains the following exports for idle.dll

00000000 characteristics
450867C8 time date stamp Thu Sep 14 04:19:20 2006
0.00 version
1 ordinal base
3 number of functions
3 number of names

ordinal hint RVA name

1 0 00001016 ?IdleUIGetLastInputTime@@YAKXZ
2 1 000010C3 ?IdleUIInit@@YAHXZ
3 2 0000111C ?IdleUITerm@@YAXXZ


1000 .data
1000 .rdata
1000 .reloc
1000 .rsrc
1000 .text
1000 Y_IDLE

It has 3 C++ functions defined, and a customized data section "Y_IDLE", I think it is the shared data section which used to store the latest user active time stamp. While what's the function protocol for these 3 function? I found a very good documentation for the C++ name mangling of different compilers at URL http://www.agner.org/optimize/ Calling conventions for different C++ compilers and operating systems
它定义了三个输出函数,同时自定义了一个程序段 Y_IDLE 相比这应该是一个数据段,用来记录从各个应用程序收集到的最新的用户消息发出的时间。 而这三个函数应该是用C++的命名规则输出的,但是这三个函数的原型是什么呢?幸好发现了一个非常好的文档,详细地描述了各种编译器的 C++ name mangling 也就是符号标的转换规则。参见 http://www.agner.org/optimize/ Calling conventions for different C++ compilers and operating systems

In fact, from the Windows 2000, WIN_VER>=0x500 there is a new function GetLastInputInfo in user32.dll, it will provide the Last user input time stamp quickly.
其实从Window2000开始,微软在 User32.dll 就提供了一个新的函数 GetLastInputInfo 它就可以用来返回用户的最后输入的时间。

* This is used to hack the Yahoo Messenger.
* compiled with VC7.1 as:
* cl -W3 -O1sy -LD -MD -D_WIN32_WINNT=0x0500 idle.cpp -Feidle.dll User32.lib


#pragma section("Y_IDLE",read,write)
int Y_IDLE = 0;

#define DllExport __declspec( dllexport )

DllExport DWORD IdleUIGetLastInputTime()
lii.cbSize = sizeof(lii);
return lii.dwTime;

DllExport INT IdleUIInit()
return TRUE;

DllExport VOID IdleUITerm()

This will be able to create a new IDLE.DLL
这样就可以知道一个新的 idle.dll , 而且它也再也不会被注入到其他的程序中了。
替换原来的 IDLE.DLL 还真不错~~~~ 工作正常。


在找到 IDLE.DLL 输出函数的原型还真花了些时间。后来才发现其实微软已经给我们提供了一个很方便的工具,那就是随Platform SDK 分发的 Dependency Walker (depends.exe) 里面有一个 Undecorate C++ functions 的功能,我们只需要用Dependency Walker 打开 IDLE.DLL 就可以看到输出函数的原型了。