Securely Storing and Retrieving Credentials with PowerShell‘s Get-Credential

Handling secure access to resources is an indispensable part of PowerShell scripting. From accessing user files to calling REST APIs, most non-trivial scripts require working with credentials. The Get-Credential cmdlet provides an easy yet powerful way to enable secure credential management in PowerShell.

Understanding PowerShell Credential Objects

The Get-Credential cmdlet prompts the user for a username and password then returns a System.Management.Automation.PSCredential object.

At a structural level, these PSCredential objects contain:

• UserName: The supplied username as a standard string
• Password: The supplied password as a System.Security.SecureString
• Domain: The optional domain context if provided

For example, running Get-Credential and entering myUser and myPassword:

UserName      Password                Domain  
--------      --------                ------
myUser      System.Security.SecureString //

We can see it encapsulates the individual components of the credentials.

Functionally, PSCredential enables several key features:

• Encapsulate identity credentials for scripts and workflows
• Allow passing around and persisting credentials securely
• Enable delegation and/or isolation of credentials
• Provide validation mechanisms for expired passwords

Understanding PSCredential objects is crucial for unlocking the capabilities of PowerShell authentication.

How SecureString Protects Passwords in Memory

A key benefit of Get-Credential is it stores the supplied password securely in memory automatically as a SecureString.

• The .NET SecureString class encrypts strings only in process memory, preventing storage on disk.
• Garbage collection wipes secret strings when they go out of scope.
• Restricts access so other processes cannot access the same SecureString instance.

This helps mitigate common vulnerabilities like:

• Plaintext password exposure in scripts or logs
• Unencrypted passwords in configuration files or databases
• Credential theft by dumping process memory

Validating the password is secured:

$cred = Get-Credential
$cred.Password

Shows only System.Security.SecureString confirming protection.

SecureStrings make credential storage transient yet usable within the context of the live process.

Transforming Standard Strings into Secure Strings

While Get-Credential handles conversion automatically, you can also create SecureString instances from plain text strings manually:

$password = ConvertTo-SecureString "myPassword" -AsPlainText -Force 

• -AsPlainText indicates providing a standard string value.
• -Force allows converting string with potential issues.

This builds secure strings without insecure variables persisting anywhere in the script.

Combined with the PSCredential constructor, we can build credentials inline without transmitting plaintext secrets:

$username = "serviceAcct"
$securePassword = ConvertTo-SecureString "340$#@LLg" -AsPlainText -Force
$credential  = New-Object System.Management.Automation.PSCredential ($username, $securePassword)  

This technique is useful for inline credential creation without hardcoding storage.

Persisting Credentials Securely on Disk

SecureString credentials exist only in memory during the active PowerShell state they were created within. To maintain credentials across sessions requires storing them on disk.

Options for secure persisting include:

• Export/import via encryption
  • Export-Clixml to encrypt objects
  • Import-Clixml to decrypt
• Store within credential manager
  • cmdkey to map credentials
  • Integrates with credential manager
• Save via .NET encryption
  • System.IO + ProtectedData
  • Custom encryption options

For example, using Export-Clixml to securely store to disk:

$cred = Get-Credential
Export-Clixml $cred secureCred.xml

This persists and encrypts credential objects portably, avoiding plain text storage.

Credential persistence allows reuse between scripts and sessions without reentering passwords continually.

Passing Managed Credentials into Remote Sessions

Credential objects can be utilized for accessing remote systems via PowerShell remoting or WinRM:

$cred = Get-Credential
Enter-PSSession Server22 -Credential $cred 

This pushes the PSCredential object through the remote session automatically.

• Mitigates insecure passwords prompting over remote connections.
• Allows managing standard credentials centrally.
• Especially useful for workgroup remoting scenarios allowing alternate credential usage.

Further, credentials can be supplied cross-script without transmitting actual secrets:

ScriptA.ps1 | ScriptB.ps1 -Credential $cred

This way each script has only the minimum viable permissions necessary.

Proper credential delegation limits exposure in case scripts or connections get compromised.

Checking for Expired Passwords

76% of data breaches involve compromised credentials according to a 2022 IBM report. Allowing expired credentials accelerates this risk.

The .PasswordExpired property on underlying .NET credentials checks status:

$cred = Get-Credential
if ($cred.GetNetworkCredential().PasswordExpired) {
   # Expired! Prompt for new password
}
else {
   # Login with credentials  
}

For service accounts, proactively check and update stored credential objects before periods of downtime like maintenance windows.

Handling password expiration ensures credentials stay aligned to access requirements before problems occur at runtime.

Mitigating Credential Theft Risks

While PowerShell manages credentials securely in memory, proper handling when transmitting credentials is crucial too.

Main risks areas include:

• Allowing plain text credential usage in scripts
• Passing insecure variables containing credentials
• Remoting credentials unencrypted
• Logging passwords accidentally

Mitigations include:

• Encrypting stored credentials on disk
• Connect with SSL/TLS transport encryption
• Consider certificate authentication rather than only password
• Isolate credential usage to specialized scripts
• Scrub logs via sanitization pipelines

Take care when passing credentials over networks and avoid typing into demos/untrusted environments.

Secure coding practices with credentials remain imperative.

Example Usage Scenarios

Proper credential management with Get-Credential unlocks many authentication use cases:

Automated logins

$cred = Get-Credential
$session = New-PSSession -ComputerName server1 -Credential $cred
Enter-PSSession $session

• Securely connects remote sessions without plaintext passwords sent over the wire

Application credential usage

$appCred = Get-Credential appUser
Invoke-RestMethod https://api.server.com/data -Credential $appCred

• Allows securely calling authenticated web APIs requiring unique non-OS identities

Delegated credential security

MasterScript.ps1 
  | GetCredentials.ps1 | Export-Clixml credentials.xml
  | ChildScript.ps1 -Cred (Import-Clixml credentials.xml)

• Provides proper isolation between components accessing resources with credentials

These examples demonstrate flexible application for automated workflows.

Recommendations and Best Practices

Based on the importance of identity credentials for access security:

Developers should:

• Use Get-Credential rather than plaintext passwords in scripts
• Implement credential isolation and delegation principles
• Encrypt any stored credentials on disk
• Validate password expiration where applicable
• Consider multifactor authentication for increased assurance

Organizations should:

• Classify credentials as sensitive resources
• Audit access by privileged accounts
• Set policies for minimum password entropy
• Establish credential rotation requirements
• Provide tools for secure password management

Proper credential hygiene limits downstream vulnerability chains.

Conclusion

Managing access credentials is an intrinsic part of PowerShell scripting functionality. The ubiquitous Get-Credential cmdlet empowers secure storage, delegation, and usage of these sensitive credentials within scripts. Combined with sound encryption and security principles, developers can build authentication workflows to access resources while preventing downstream credential theft. Treat identity credentials as a precious resource and instrument the proper controls around management via Get-Credential and PowerShell will reward you with robust access functionality.