Mastering Privilege Escalation on Windows with the Ansible Runas Become Plugin

The orchestration of Windows environments via Ansible requires a nuanced understanding of how identity and access management operate within the Microsoft ecosystem. Unlike Linux, where the sudo (superuser do) mechanism allows a user to execute a command with the security privileges of another user—most commonly the root user—Windows utilizes a complex system of access tokens, security identifiers (SIDs), and user impersonation. To bridge this gap, Ansible implements the runas become plugin. This mechanism allows administrators to transition from the initial connection user (the account used for the WinRM or SSH session) to a target account with the necessary privileges to perform administrative tasks, such as installing software, modifying system registries, or accessing protected network shares.

The fundamental objective of using become on Windows is to ensure that tasks are executed within the correct security context. Because Windows does not possess a singular, universal "root" account in the way Unix-like systems do, the runas plugin acts as the engine that creates a new process under the target user's security context. This is critical for bypassing the limitations of a standard WinRM session, where the initial user may be restricted by User Account Control (UAC) or lack the specific permissions required for high-level system modifications.

The Architectural Divergence of Windows and Linux Privilege Escalation

To implement runas effectively, one must first understand the technical reasons why Windows privilege escalation differs from the standard Linux become experience.

On Linux, the process of becoming root is generally straightforward: the sudo plugin manages the transition, and the system defaults to the root user if no other user is specified. Windows, however, operates on a model of user impersonation and access tokens. The runas plugin does not simply "switch" users; it spawns a new process that inherits the security token of the specified target account.

The technical and administrative layers of this difference are summarized in the following table:

The impact of this divergence is significant for the Ansible operator. In a Linux playbook, become: true is often sufficient to execute a task as root. On Windows, attempting to use become: true without specifying a become_user will result in a fatal error. This is because the runas plugin cannot assume a default administrative account, as the "Administrator" account name may vary or may be disabled in favor of specific domain admin accounts.

Technical Configuration of the Runas Become Plugin

The runas plugin is the primary tool for achieving privilege escalation on Windows hosts. It allows the execution of modules as different users, including local accounts, domain accounts, or specialized service accounts.

Implementation at the Task Level

For granular control, become can be applied to individual tasks. This is the preferred method when only a small subset of operations requires elevated privileges, thereby adhering to the principle of least privilege.

To implement this, the following directives must be present: - become: true: This tells Ansible to activate the escalation mechanism for the specific task. - become_method: runas: This explicitly defines the plugin to be used. While runas is the standard for Windows, specifying it ensures clarity and prevents conflicts in multi-platform environments. - become_user: The target account (e.g., Administrator or MYDOMAIN\svc_myapp). - become_pass: The password for the target account, which should be securely stored using Ansible Vault.

Implementation at the Play Level

When an entire sequence of tasks requires administrative access—such as installing a web server and configuring directories—it is more efficient to set become at the play level. By defining these variables in the play header or within group_vars, every task in the play will automatically execute as the specified user.

Example play-level configuration: - become: true - become_method: runas - become_user: Administrator - ansible_become_pass: Defined via vault.

This approach simplifies the playbook, removing the need to repeat the become directives for every module call, such as win_feature for installing IIS or win_service for managing the W3SVC service.

Advanced Credential Management and Outbound Authentication

One of the most complex challenges in Windows automation is the "double-hop" problem. This occurs when a remote user connects to a Windows server (the first hop) and then attempts to access a network resource, such as a file share (the second hop), using the same credentials. By default, Windows does not delegate credentials to the second hop for security reasons.

Resolving the Double-Hop with Become Flags

The runas plugin provides a solution through become_flags. These flags allow the user to specify the logon type and how credentials are handled for outbound authentication.

A critical configuration for accessing remote shares (e.g., using win_copy to move a file from \\fs\share\app\app.config to a local destination) involves the following flags: - logon_type=new_credentials: This tells Windows to use the credentials explicitly provided in the become_pass for the network session. - logon_flags=netcredentials_only: This ensures that the credentials are used specifically for network authentication attempts.

In this scenario, the become_user and become_pass are typically set to the same values as the ansible_user and ansible_password. This bypasses the limitation of the WinRM session by explicitly re-authenticating for the outbound request, effectively enabling the "double-hop" functionality.

Managing Domain Accounts and Service Identities

In Active Directory (AD) environments, privilege escalation often involves domain accounts rather than local administrators. The runas plugin is fully compatible with domain identities.

Domain Service Accounts

When running application setups (e.g., executing a PowerShell script like C:\scripts\setup-app.ps1), it is common to use a domain service account. This ensures the application runs with the correct identity for accessing database servers or other domain resources.

Technical requirement: When using domain accounts, the become_user must be specified in the format DOMAIN\username. Additionally, the become_flags can be set to logon_type=batch to ensure the process starts as a batch job, which is often required for non-interactive service account execution.

Domain Administrator Accounts

For high-level tasks, such as configuring a scheduled task (community.windows.win_scheduled_task), a domain administrator account may be required. The process remains the same as local escalation, but the security context is shifted to the domain's administrative tier. This allows the creation of tasks that can run as other users (e.g., MYDOMAIN\svc_backup) while the creation process itself is authorized by the domain admin.

Comprehensive Guide to Runas Logon Types

The become_flags parameter is the primary mechanism for controlling how the target user is logged into the system. Different scenarios require different logon types to avoid "Access Denied" errors.

• Interactive Logon: This is the default behavior. It is used for tasks that simulate a user logging into the machine.
• Batch Logon: Specified via logon_type=batch. This is essential for service accounts that do not have a full interactive profile but need to execute scripts.
• New Credentials: Specified via logon_type=new_credentials. This is used specifically for outbound authentication to remote servers, solving the double-hop issue.

Troubleshooting and Diagnostic Strategies

Privilege escalation on Windows is prone to specific failures related to security policies and registry settings. When a runas task fails, a systematic diagnostic approach is required.

Common Error Analysis

The following table maps common runas error messages to their technical causes and solutions:

The UAC and Registry Fix

A frequent cause of "Access Denied" errors for local administrators over WinRM is the User Account Control (UAC) filter. When connecting remotely, Windows may filter out the administrative token, even if the user is a member of the Administrators group.

To resolve this, the LocalAccountTokenFilterPolicy registry key must be set to 1. This allows local administrator accounts to obtain full administrative tokens over remote connections, ensuring that the runas plugin can successfully elevate the process.

Diagnostic Playbook Pattern

To identify where a failure occurs, administrators should use a diagnostic playbook that tests identity at three stages: 1. Testing without become: Using ansible.windows.win_whoami to verify the base connection user. 2. Testing with runas: Using become: true with win_whoami to verify that the transition to the administrative user is successful. 3. Verifying Privileges: Using ansible.windows.win_command: whoami /priv to check if the resulting token actually possesses the required administrative privileges.

Summary of Configuration Requirements

To ensure a successful deployment of the runas plugin, the following technical requirements must be met:

• Mandatory Parameters: On Windows, become_user must be explicitly provided. There is no default "root" equivalent that Ansible can assume.
• Credential Security: become_pass must be provided for the runas method to function.
• Connectivity: The target host must be configured for WinRM, and the initial user must have the right to initiate the runas process.
• Environment: For domain users, the DOMAIN\user syntax is required.

Conclusion

The use of the runas become plugin transforms Ansible from a basic remote execution tool into a powerful orchestration engine for Windows environments. By mastering the distinctions between Linux and Windows privilege models, administrators can overcome the limitations of WinRM sessions and the complexities of the double-hop problem. The ability to precisely control the security context through become_flags and logon_type allows for the secure management of everything from local IIS installations to complex domain-wide service account configurations. While the requirement to explicitly define become_user adds a layer of configuration overhead compared to Linux, it provides the necessary specificity required by the Windows security architecture. When combined with the LocalAccountTokenFilterPolicy registry adjustment and secure vaulting of credentials, the runas plugin provides a robust and scalable framework for Windows automation.

Sources

1. How to Use Ansible Become with the Windows Runas Plugin
2. Become has different requirements on Windows #78599
3. Making Double-Hop Windows Ansible