Introduction

The ability to add or remove users from Windows’ Local Administrators group is a crucial administrative task. However, malicious actors often exploit this privilege to gain elevated access to a system, creating an administrative account for themselves or others to maintain persistence. If an attacker manages to add their own user account to the Local Administrators group, they can effectively control the system, install malware, and exfiltrate sensitive data with minimal detection.

In this post, we’ll explore:

• How adding a user to the Local Administrators group works on Windows
• Why attackers target this action
• Techniques used by attackers to silently add themselves to the Administrators group
• How to detect suspicious activity related to user additions
• How you can detect it in Logstail, trigger an alert, and respond automatically using Logstail SOAR.

What is the Local Administrators Group?

The Local Administrators group in Windows provides a set of users with full control over the local machine. Members of this group have the ability to:

• Install software and updates
• Modify system settings
• Access sensitive data
• Execute commands with elevated privileges

In an enterprise environment, only trusted users (such as IT administrators) should have membership in this group. Therefore, any unauthorized addition to this group signals a potential security issue.

Why Do Attackers Add Users to the Local Administrators Group?

Attackers add themselves or other users to the Local Administrators group to maintain persistent access to a system. This is one of the most common ways attackers ensure they can return to a compromised machine, even after a reboot or when their original access method (such as a backdoor or exploit) is removed.

Some reasons attackers may add users to the Administrators group include:

• Persistence: An attacker who adds themselves as an administrator can easily return to the system even after the original attack vector is closed or detected.
• Privilege Escalation: Gaining administrative privileges on a system may help an attacker escalate their access from a low-privilege user to one with full system control.
• Lateral Movement: If an attacker is able to add an account to the Administrators group, they can use that account to move laterally across a network and compromise other systems with ease.

How Attackers Gain Admin Access

Attackers can add a user to the Local Administrators group via several methods, including:

1.Command Line (net localgroup): One of the most straightforward ways is using the net localgroup command, which is native to Windows. An attacker can execute this command to add a user to the Administrators group.

PoC Command:

2.PowerShell: Using PowerShell, attackers can execute scripts to add a user to the Local Administrators group. The command would look like this:

3.Third-Party Tools: Attackers may also use third-party tools, such as Mimikatz or other post-exploitation frameworks, to silently add a user to the Administrators group without generating immediate alarms.

Suspicious User Behavior

Detection doesn’t end with the act of adding a user — security teams should also monitor what that user does afterward. Suspicious behavior following privilege escalation can indicate an active compromise.

For example, if a newly created user immediately starts modifying system settings, disables antivirus protections, or installs software after hours, this could be an attacker at work. Similarly, if no support ticket or documentation explains the account creation and privilege assignment, it raises serious concerns.

Naming conventions are another red flag. Attackers often create accounts like helpdesk_support, svc_backup, or admin_temp to blend in with existing service accounts. They might also hide these accounts from the login screen, disable banners, or spoof timestamps to make them look older and more legitimate.

Continuous behavioral analysis of privileged users helps surface stealthy activity that static rule-based monitoring might miss. Combining this with detection of administrative group changes gives organizations a layered defense approach.

Example Attack Scenario

Let’s say an attacker gains access to a system. Instead of immediately dropping obvious malware and risking instant detection, they move more stealthily:

• The attacker adds a new user account (e.g., testuser1, helpdesk_support) to the local Administrators group.

• What this command do:

• This grants them full control over the machine without triggering traditional malware alerts.
• They might set this account to have a disabled login banner, hide the user from the login screen, or backdate timestamps to blend in with legitimate accounts.
• With administrative rights, the attacker can:

  • Disable or modify security tools (AV/EDR).

  • Deploy malware later with elevated permissions.

  • Create scheduled tasks or services under SYSTEM context.

  • Exfiltrate sensitive data or move laterally across the network.

How to Detect and Respond to Admin User Additions

To detect such unauthorized additions, Logstail can be configured with a real-time Lucene query:

This query looks for the following patterns:

• Commands that include the localgroup keyword (commonly used for adding or removing users from groups)
• Add-LocalGroupMember PowerShell cmdlets targeting the administrators group

Once detected, the system can trigger an alert, which could be used to notify administrators or trigger an automated response such as disabling the user account or isolating the affected system from the network.

Alert in Logstail SOAR

Logstail continuously monitors system activity by utilizing powerful, Lucene-based queries that are specifically designed to detect potentially malicious actions, such as unauthorized additions to the Local Administrators group. These queries act as the backbone for preconfigured alert rules, which automatically flag suspicious behavior in real-time. When an action triggers one of these queries — for instance, an unexpected change to user privileges or abnormal system behavior — an alert is generated.

This alert is then immediately forwarded to the Logstail SOAR (Security Orchestration, Automation, and Response) dashboard for further review. Within SOAR, security analysts can dive deep into the alert’s details, including the specific Lucene query that was triggered, the process command line that matched the suspicious pattern, and the exact endpoint where the anomaly occurred. This enables quick investigation and response to potential security threats, with the associated logs readily available for a comprehensive analysis of the event.

What Happens When It’s Triggered?

When this rule fires, it raises an alert in the Logstail SOAR dashboard, giving you full context:

1. Agent Name : The machine where it was detected
2. Alert Name: User Added to Local Administrators Group
3. Severity: The severity of the specific alert -Medium
4. Timestamp: When the event occured
5. View Log: Direct link to the full raw event with the Details (i) feature.

In the SOAR interface, these elements are displayed in a structured format for rapid triage making it easy for analysts to quickly identify and assess critical aspects of the alert.

By providing full visibility into the event, SOAR ensures security teams can act swiftly and decisively to investigate and contain threats before they escalate.

Log details can be checked:

Automated Response Using a Logstail SOAR Playbook

It’s not enough to simply recognize a threat; you also need to act quickly to prevent the attack from spreading. Logstail SOAR playbooks can help with that.

A playbook is a collection of automated procedures that are set off by particular alarms. Without requiring human participation, Logstail may automatically execute a pre-programmed playbook to look into, contain, and react to the “User Added to Local Administrators Group” alert.

Playbook Action Demonstration: Remove Admin User 

The automated playbook performs one crucial task:

• It removes the user form the admin group

When the alert is triggered, Logstail SOAR sends a command to the affected endpoint, through the Logstail Agent, to remove the admin user— stopping any further execution giving the analyst a chance to review it safely.

This provides team members with immediate visibility into the compromised system’s activity, allowing for rapid adjustments in response to potential threat escalation or multi-stage attacks.

Here, we can observe the actions performed by the playbook:

Before the playbooks action :

After executing the playbook’s actions, it is confirmed that the user has been successfully removed from the Administrators’ group.

Final Thoughts

Malicious Local Administrator Addition is a serious security concern, as it allows attackers to gain elevated privileges on a system, enabling them to execute a wide range of malicious actions with full control. It’s crucial to not only log this type of activity, but to also continuously monitor, detect, and respond to any unauthorized changes in local administrator groups.

With tools like Logstail, you can stay ahead of potential breaches by:

• Detecting unauthorized additions to local administrator groups in real-time

• Automating response with SOAR playbooks to quickly remediate incidents

• Collecting comprehensive forensic data to aid in investigations

• Actively hunting for signs of privilege escalation across endpoints

By integrating this level of visibility and automation, you shift from a reactive to a proactive defense posture, ensuring that you can prevent attackers from exploiting administrative access before they cause significant damage.

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