PowerShell execution policy is useful as a safety and configuration feature, but it is not a security boundary: Microsoft describes it as “defense in depth,” not a control that can reliably stop a determined user or attacker from running code. The teaching trap is treating a policy label such as AllSigned or RemoteSigned as proof that scripts are safe—or that unauthorized code cannot run.
What execution policy controls—and what it does not
Execution policy governs conditions for loading PowerShell configuration files and scripts. It can help prevent accidental policy violations and discourage unsafe script use, but it does not establish which code a capable user is allowed to execute. Microsoft explains that script-file restrictions can be bypassed by typing the script contents at the command line. A policy therefore cannot certify a script as benign or serve as a dependable barrier against someone who can run commands.
That distinction matters when teaching PowerShell: describe the behavior each setting changes, then explain separately how an organization enforces which software may run. Microsoft’s execution policy documentation calls the feature defense in depth.
What each policy mode actually does
| Policy | Practical effect | Important limit |
|---|---|---|
| AllSigned | Requires scripts and configuration files—including locally created ones—to be signed by a trusted publisher. PowerShell may prompt when a publisher is not yet classified as trusted or untrusted. | A valid signature identifies a publisher and detects changes; it does not make malicious code safe. |
| RemoteSigned | Requires downloaded scripts to be signed by a trusted publisher. Locally written scripts do not need signatures. | Windows’ downloaded-file marking affects how a file is treated. Some download methods may not mark a file as Internet-origin, and an unsigned downloaded file may run if it is unblocked. |
| Restricted | Allows individual commands but blocks script files, including profile, module script, formatting, and configuration files. | Microsoft documents it as the default for Windows client computers; that does not make it an enforcement boundary. |
| Unrestricted | Allows unsigned scripts, while warning for scripts and configuration files outside the local intranet zone. | A warning is not a block. |
| Bypass | Blocks nothing and displays no warnings or prompts. | Microsoft describes it for situations where PowerShell is embedded in a larger application that supplies its own security model. |
| Undefined / Default | When all scopes are Undefined, the platform’s documented default applies: Restricted on Windows client computers and RemoteSigned on Windows servers. | Do not assume one default applies to every Windows role or non-Windows system. |
These behaviors are documented in Microsoft’s policy reference. In particular, choosing AllSigned or RemoteSigned changes how PowerShell handles files; it does not prove that allowed scripts are trustworthy.
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How scope and precedence change the effective policy
A policy can be set for the current process, current user, local machine, or through Group Policy. Process scope applies only to the current PowerShell session. Group Policy settings at MachinePolicy or UserPolicy take precedence over locally set policies, so a local change may not determine the effective result.
Check both the configured scopes and the effective policy instead of inferring one from a prior command:
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If the result differs from what you expected, check whether a Group Policy scope is set and confirm which PowerShell host and version you opened.
Windows PowerShell 5.1 (powershell.exe) and PowerShell 6.0 and later (pwsh.exe) store execution policy settings separately; a setting in one does not automatically control the other. The scope and host details are covered in the Set-ExecutionPolicy reference.
Why Windows and non-Windows behavior differ
Execution policy is a Windows-specific mechanism. Non-Windows PowerShell does not implement Windows security zones, and Set-ExecutionPolicy is unsupported there. The reported Unrestricted value behaves like Bypass on non-Windows platforms. Do not transfer Windows assumptions about downloaded-file markings or policy defaults to PowerShell on another operating system. See Microsoft’s platform notes.
What to consider when code execution must be restricted
If the requirement is to prevent unauthorized code from running, evaluate controls designed for enforcement rather than relying on execution policy. Microsoft identifies App Control for Business and constrained language mode with App Control for Business as security features, in contrast to execution policy’s defense-in-depth role. The appropriate control depends on the platform, operational requirements, and threat model; no single setting is a universal replacement.
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MITRE ATT&CK describes execution-prevention measures such as application control and script blocking. Its examples include AppLocker or WDAC on Windows, SELinux or AppArmor on Linux, signed or pre-approved applications, and restricting executables in user-writable directories. NIST’s SP 800-167 guide to application whitelisting defines the approach as maintaining a list of applications and components authorized for organizational use, and discusses planning and implementation across the deployment lifecycle.
These are organizational control choices, not a reason to treat a signing prompt or a policy setting as a guarantee. Microsoft’s overview of PowerShell security features distinguishes security features from defense-in-depth features.
A related lesson: execution policy does not prevent command injection
Execution policy governs PowerShell’s handling of scripts and configuration files; command injection is a separate flaw in software that constructs an operating-system command from externally influenced input without correctly neutralizing characters that alter the command. Changing execution policy does not fix unsafe command construction.
If calling an operating-system command is unavoidable, OWASP recommends separating data from commands through parameterization, allowing only approved commands, and validating arguments. A denylist of known-bad patterns is easy to bypass and should not be the primary defense. See OWASP’s OS Command Injection Defense Cheat Sheet and Input Validation Cheat Sheet.
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