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Enumeration of Privileged Local Groups Membership

Elastic Stack Serverless Security

Identifies instances of an unusual process enumerating built-in Windows privileged local groups membership like Administrators or Remote Desktop users.

Rule type: eql

Rule indices:

  • winlogbeat-*
  • logs-system.*

Severity: medium

Risk score: 43

Runs every: 5m

Searches indices from: now-9m (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

References: None

Tags:

  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Discovery

Version: 4

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

After successfully compromising an environment, attackers may try to gain situational awareness to plan their next steps.
This can happen by running commands to enumerate network resources, users, connections, files, and installed security
software.

This rule looks for the enumeration of privileged local groups' membership by suspicious processes, and excludes known
legitimate utilities and programs installed. Attackers can use this information to decide the next steps of the attack,
such as mapping targets for credential compromise and other post-exploitation activities.

  • Identify the process, host and user involved on the event.
  • Investigate the process execution chain (parent process tree) for unknown processes. Examine their executable files
    for prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
  • Investigate other alerts associated with the user/host during the past 48 hours.
  • Investigate abnormal behaviors observed using the account, such as commands executed, files created or modified, and
    network connections.
  • Retrieve the process executable and determine if it is malicious:
    • Check if the file belongs to the operating system or has a valid digital signature.
    • Use a private sandboxed malware analysis system to perform analysis.
      • Observe and collect information about the following activities:
        • Attempts to contact external domains and addresses.
        • File and registry access, modification, and creation activities.
        • Service creation and launch activities.
        • Scheduled tasks creation.
  • Discovery activities are not inherently malicious if they occur in isolation. As long as the analyst did not identify
    suspicious activity related to the user or host, such alerts can be dismissed.
  • If this activity is expected and noisy in your environment, consider adding exceptions — preferably with a combination
    of user and command line conditions.
  • Initiate the incident response process based on the outcome of the triage.
  • Isolate the involved hosts to prevent further post-compromise behavior.
  • Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are
    identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business
    systems, and web services.
  • Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and
    malware components.
  • Determine the initial vector abused by the attacker and take action to prevent reinfection via the same vector.
  • Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the
    mean time to respond (MTTR).

The 'Audit Security Group Management' audit policy must be configured (Success).
Steps to implement the logging policy with with Advanced Audit Configuration:

Computer Configuration >
Policies >
Windows Settings >
Security Settings >
Advanced Audit Policies Configuration >
Audit Policies >
Account Management >
Audit Security Group Management (Success)

Microsoft introduced the event used in this detection rule on Windows 10 and Windows Server 2016 or later operating systems.

If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define event.ingested and default fallback for EQL rules was not added until 8.2, so you will need to add a custom pipeline to populate event.ingested to @timestamp for this rule to work.

Rule query

iam where event.action == "user-member-enumerated" and

 /* noisy and usual legit processes excluded */
 not winlog.event_data.CallerProcessName:
              ("?:\\Windows\\System32\\VSSVC.exe",
               "?:\\Windows\\System32\\SearchIndexer.exe",
               "?:\\Windows\\System32\\CompatTelRunner.exe",
               "?:\\Windows\\System32\\oobe\\msoobe.exe",
               "?:\\Windows\\System32\\net1.exe",
               "?:\\Windows\\System32\\svchost.exe",
               "?:\\Windows\\System32\\Netplwiz.exe",
               "?:\\Windows\\System32\\msiexec.exe",
               "?:\\Windows\\System32\\CloudExperienceHostBroker.exe",
               "?:\\Windows\\System32\\wbem\\WmiPrvSE.exe",
               "?:\\Windows\\System32\\SrTasks.exe",
               "?:\\Windows\\System32\\lsass.exe",
               "?:\\Windows\\System32\\diskshadow.exe",
               "?:\\Windows\\System32\\dfsrs.exe",
               "?:\\Program Files\\*.exe",
               "?:\\Program Files (x86)\\*.exe") and
  /* privileged local groups */
 (group.name:("admin*","RemoteDesktopUsers") or
  winlog.event_data.TargetSid:("S-1-5-32-544","S-1-5-32-555"))

Framework: MITRE ATT&CKTM