What is PowerShell Execution Policy?
PowerShell Execution Policy is a security feature that determines the conditions under which PowerShell scripts can run. It acts as a safeguard against potentially malicious scripts and helps mitigate security risks associated with arbitrary code execution.
Levels of Execution Policy
PowerShell offers several levels of Execution Policy, ranging from unrestricted, allowing all scripts to run without any restrictions, to restricted, which prohibits the execution of any script.
Security Implications
Understanding the security implications of each Execution Policy level is crucial for maintaining a secure environment:
Unrestricted: While sometimes required for development and testing, this level poses the highest security risk as it allows execution of all scripts, including those obtained from the internet or other untrusted sources, without any validation.
Restricted: This level provides maximum security by disallowing script execution altogether. While this ensures safety, it may hinder productivity as legitimate scripts won't run unless the policy is changed.
RemoteSigned: Scripts downloaded from the internet must be digitally signed by a trusted publisher to execute. Locally created scripts can still run without restrictions.
AllSigned: Similar to RemoteSigned, but all scripts, regardless of origin, must be digitally signed by a trusted publisher. This ensures that all scripts are authenticated before execution, minimizing the risk of running malicious code.
Bypass: This level allows all scripts to run, bypassing Execution Policy restrictions entirely. This should be used with extreme caution and even then it should only be used temporarily.
Undefined: There is no execution policy set within the current scope. Possible scopes include MachinePolicy, UserPolicy, CurrentUser, Process and LocalMachine.
Best Practices
To maintain a secure PowerShell environment, consider the following best practices:
Use the principle of least privilege: Choose the most restrictive Execution Policy that still allows necessary scripts to run. It's normal to have a mix of execution policies across different users and devices, based on the requirements of the organisation.
Digitally sign all required scripts: Signing scripts with a trusted certificate helps verify their authenticity and allows for the use of stricter execution policies.
Regularly review and update policies: Periodically review Execution Policies to ensure they align with security requirements and make adjustments as necessary.
Block Powershell scripts received via email: Regardless of execution policy, there is rarely a business justification for allowing end users to receive Powershell scripts as email attachments. Configure the mail filtering/attachment handling solution to block Powershell script files.
PowerShell Execution Policy is a critical component of PowerShell security, providing a layer of defense against malicious scripts. By understanding the different policy levels and implementing best practices, organizations can maintain a secure PowerShell environment without sacrificing productivity.
More Information:
Learn.microsoft.com - About Execution Policies