PowerShell Script Security

Execution Policies

Execution policies in PowerShell control whether scripts are allowed to run and under what circumstances. These policies help prevent the execution of malicious or unauthorized scripts and protect the system from potential security risks.

There are different execution policy levels:

• Restricted: No scripts are allowed to run. Only individual commands can be executed interactively.
• AllSigned: Scripts can run, but they must be digitally signed by a trusted publisher.
• RemoteSigned: Local scripts can run without a signature, but any script downloaded from the internet must be signed by a trusted publisher.
• Unrestricted: All scripts can run without any restrictions. This mode can be risky and should be used with caution.

To set the execution policy, open an elevated PowerShell console and use the Set-ExecutionPolicy cmdlet:

Set-ExecutionPolicy RemoteSigned

Code Signing and Digital Signatures

Code signing involves digitally signing your PowerShell scripts to prove their authenticity and integrity. Digital signatures provide assurance that the script comes from a known and trusted source and has not been tampered with.

To sign a script, you need a code signing certificate from a trusted certificate authority (CA). You can use the Set-AuthenticodeSignature cmdlet to sign scripts:

Set-AuthenticodeSignature -FilePath C:\Scripts\MyScript.ps1 -Certificate (Get-ChildItem Cert:\CurrentUser\My -CodeSigningCert)

By signing your scripts, users can verify the script's publisher and detect any changes made to the script after it was signed.

Best Practices for Secure Scripting

Here are some best practices to enhance the security of your PowerShell scripts:

1. Use Least Privilege: Run scripts with the minimum privileges required. Avoid running scripts with administrative privileges unless necessary.

2. Validate Input: Ensure that any user-provided input is properly validated and sanitized to prevent code injection and other security vulnerabilities.

3. Secure Credential Handling: Avoid hardcoding credentials in your scripts. Instead, use techniques like credential encryption or securely prompt for credentials when needed.

4. Audit Script Changes: Keep track of script changes, and only allow authorized users to modify scripts.

5. Regular Updates: Keep PowerShell and its modules up to date to benefit from security patches and bug fixes.

6. Limited Use of Execution Policies: Use execution policies judiciously, opting for more restrictive settings whenever possible.

7. Centralized Script Repository: Store scripts in a centralized and secure location accessible only to authorized users.

8. Code Review: Conduct regular code reviews to identify potential security flaws and improve script quality.

9. Use Modules: Encapsulate code in reusable modules, reducing the risk of errors and facilitating maintenance.

10. Secure Remoting: Use PowerShell remoting securely with properly configured authentication and encryption.

Always be cautious when running scripts from unknown sources, and ensure that you trust the source before enabling the execution of unsigned scripts.

By adhering to PowerShell script security best practices, you can minimize potential risks and maintain a secure scripting environment. Combining execution policies, code signing, and secure coding practices helps protect your system and data from malicious or unintentional script behavior.