Analyzing PowerShell Scripts
1. Understanding PowerShell Scripts:
Threat Actor Use:
PowerShell scripts are popular among threat actors for post-exploitation activities.
Identifying PowerShell Scripts:
Familiarity with PowerShell syntax is crucial. Common keywords include:
function
: Defines a function.Set-Alias
: Creates an alias for a cmdlet or function.IEX (Invoke-Expression)
: Executes a string or script passed to it.
2. Tools for Analysis:
Text Editor for Static Analysis:
View the script in a text editor for basic, static analysis.
PowerShell ISE (Integrated Scripting Environment):
An IDE tool by Microsoft for developing and debugging PowerShell scripts.
Pre-installed on Windows, useful for dynamic analysis.
3. Practical Analysis:
Sample File Analysis: (say)
Analyze
re_test_dlx.ps1
using PowerShell ISE.Initial Check:
Use tools like Detect It Easy to verify the script is in plain text format.
Loading the Script:
Open the script in PowerShell ISE.
Long lines in the script may require horizontal scrolling as PowerShell ISE lacks word wrapping.
Beautifying the Script:
Break down complex, long lines to improve readability.
Use code formatting techniques like:
Curly Braces (
{}
): Expand functions based on these brackets.Semi-Colons (
;
): Break down lines at each semi-colon.
Alternatively, use external code beautification tools for better results.
Identifying Functions:
Look for functions like
encode
and analyze their content.Example: A function that decodes a Base64 string can be manually decoded using tools like CyberChef.
4. Debugging the Script:
Setting Breakpoints:
Use F9 to set breakpoints.
Example: Set a breakpoint at the Set-Alias command to intercept script execution.
Debugging Process:
Set-Alias Command:
Associates
XXX
as an alias for theIEX
function, enablingXXX
to execute scripts.
Execution Interception:
Replace
IEX
withWrite-Host
to output the script to the console instead of executing it.
Handling Pipes (
|
):Pipes are used to pass the output from one command to another.
Alternative Debugging:
Break the script at pipes and introduce variables to capture intermediate outputs.
Example: Capture and inspect the content of the variable
temp
before execution.
5. Final Analysis:
Decrypted Data:
The decrypted data reveals another PowerShell script designed to download and execute an executable from
www.evil.com
.
Resources:
For further analysis, refer to:
PowerShell ISE for debugging.
Microsoft's Website for PowerShell syntax and standard functions.
Key Takeaways:
PowerShell ISE:
A powerful tool for dynamically analyzing and debugging PowerShell scripts.
Debugging Techniques:
Intercepting script execution and replacing key functions can reveal hidden behaviors.
Use of External Tools:
Tools like CyberChef are essential for decoding and analyzing encoded data within scripts.
Understanding Syntax:
Familiarity with PowerShell syntax is critical for effective script analysis and detection of malicious activities.
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