Boosting PowerShell Security: Expert Tips for Ironclad Protection

Introduction to PowerShell

PowerShell, a versatile command-line tool and scripting language crafted by Microsoft, has been a cornerstone of Windows operating systems since Windows 7. Its prowess in offering extensive control over system configurations, coupled with a user-friendly interface, makes it an indispensable asset in system management. However, these very features also render it a favored tool for attackers seeking to exploit systems post-compromise.

PowerShell as an Attack Vector

Attackers frequently exploit PowerShell due to its deep-seated integration with Windows. This integration enables attackers to masquerade as regular users, execute harmful commands, and evade security protocols. Furthermore, PowerShell’s capability to run processes in memory makes it an ideal candidate for fileless malware attacks, which are notoriously difficult to detect and mitigate.

Securing PowerShell

To counteract these threats, it’s imperative to implement PowerShell security hardening measures. Here are some pivotal steps to fortify PowerShell:

PowerShell Constrained Language Mode (CLM)

PowerShell CLM curtails access to sensitive components used to invoke Windows APIs. Upon activation, it permits the use of cmdlets but obstructs commands that interact with APIs. Here are some restrictions enforced by CLM:

Prevents the use of wildcards (*, ?) to search for script and manifest files of a PowerShell module.
Blocks COM objects to hinder attackers from calling Win32 APIs.
Permits only whitelisted .NET libraries.
Obstructs the Add-Type cmdlet that allows defining .NET Core classes.
Precludes the use of PowerShell classes and variable type conversions.
Blocks dot-sourcing, which allows referencing code between language modes.
Prevents the display of commands that cannot be executed in a language mode.
Blocks XAML-based workflows unless they are trusted.
Disables the SupportedCommand parameter for the Import-LocalizedData cmdlet.
Allows the Invoke-Expression cmdlet to run only in CLM mode.
Blocks the Set-PSBreakpoint cmdlet using UMCI.
Allows command completion only in CLM mode.
Disables DSC Configuration keywords.
Does not permit supported commands and scripts in the DATA section.
Blocks the use of the Start-Job cmdlet if the system is locked down.

Logging PowerShell Activities

To uncover malicious activities, it’s vital to log PowerShell actions. This can be activated through the following policies:

Module Logging: Logs details of sequentially executed commands. Activated through the ‘Turn on Module Logging’ policy.
Script Logging: Records all code blocks within a script file and logs all script activities. Activated through the ‘Turn on PowerShell Script Block Logging’ policy.
Transcription: Captures all input and output of PowerShell sessions. Activated through the ‘Turn on PowerShell Transcription’ policy.

Conclusion

Securing PowerShell is a pivotal step in safeguarding your systems from sophisticated threats. By implementing PowerShell CLM and enabling comprehensive logging, you can substantially bolster your system’s security posture. For more in-depth guidance, refer to the official PowerShell documentation.