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PowerShell Script with Token Impersonation Capabilitiesedit

Detects scripts that contain PowerShell functions, structures, or Windows API functions related to token impersonation/theft. Attackers may duplicate then impersonate another user’s token to escalate privileges and bypass access controls.

Rule type: query

Rule indices:

  • winlogbeat-*
  • logs-windows.powershell*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Domain: Endpoint
  • OS: Windows
  • Use Case: Threat Detection
  • Tactic: Privilege Escalation
  • Data Source: PowerShell Logs

Version: 11

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guideedit

Triage and analysis

Investigating PowerShell Script with Token Impersonation Capabilities

PowerShell is one of the main tools system administrators use for automation, report routines, and other tasks. This makes it available for use in various environments, and creates an attractive way for attackers to execute code.

Adversaries can abuse PowerShell to perform token impersonation, which involves duplicating and impersonating another user’s token to escalate privileges and bypass access controls. This rule identifies scripts containing PowerShell functions, structures, or Windows API functions related to token impersonation/theft.

Note: This investigation guide uses the Osquery Markdown Plugin introduced in Elastic Stack version 8.5.0. Older Elastic Stack versions will display unrendered Markdown in this guide.

Possible investigation steps

  • Examine the script content that triggered the detection; look for suspicious DLL imports, collection or exfiltration capabilities, suspicious functions, encoded or compressed data, and other potentially malicious characteristics.
  • Investigate the script 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.
  • Examine PowerShell process creation and script block logs to identify command line arguments or hardcoded information that can indicate which user was the target of the impersonation.
  • Investigate any abnormal behavior by the subject process (PowerShell), such as network connections, registry or file modifications, and any spawned child processes.
  • Evaluate whether the user needs to use PowerShell to complete tasks.
  • Examine the host for derived artifacts that indicate suspicious activities:
  • Analyze the script using a private sandboxed analysis system.
  • Observe and collect information about the following activities in both the sandbox and the alert subject host:
  • Attempts to contact external domains and addresses.
  • Use the Elastic Defend network events to determine domains and addresses contacted by the subject process by filtering by the process' process.entity_id.
  • Examine the DNS cache for suspicious or anomalous entries.
  • !{osquery{"label":"Osquery - Retrieve DNS Cache","query":"SELECT * FROM dns_cache"}}
  • Use the Elastic Defend registry events to examine registry keys accessed, modified, or created by the related processes in the process tree.
  • Examine the host services for suspicious or anomalous entries.
  • !{osquery{"label":"Osquery - Retrieve All Services","query":"SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services"}}
  • !{osquery{"label":"Osquery - Retrieve Services Running on User Accounts","query":"SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services WHERE\nNOT (user_account LIKE %LocalSystem OR user_account LIKE %LocalService OR user_account LIKE %NetworkService OR\nuser_account == null)\n"}}
  • !{osquery{"label":"Osquery - Retrieve Service Unsigned Executables with Virustotal Link","query":"SELECT concat(https://www.virustotal.com/gui/file/, sha1) AS VtLink, name, description, start_type, status, pid,\nservices.path FROM services JOIN authenticode ON services.path = authenticode.path OR services.module_path =\nauthenticode.path JOIN hash ON services.path = hash.path WHERE authenticode.result != trusted\n"}}
  • Retrieve the files' SHA-256 hash values using the PowerShell Get-FileHash cmdlet and search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
  • Investigate potentially compromised accounts. Analysts can do this by searching for login events (for example, 4624) to the target host after the registry modification.

False positive analysis

  • Regular users should not need to impersonate other users, which makes false positives unlikely. In the case of authorized benign true positives (B-TPs), exceptions can be added.

Related Rules

  • PowerShell PSReflect Script - 56f2e9b5-4803-4e44-a0a4-a52dc79d57fe
  • Potential Process Injection via PowerShell - 2e29e96a-b67c-455a-afe4-de6183431d0d

Response and Remediation

  • Initiate the incident response process based on the outcome of the triage.
  • Isolate the involved hosts to prevent further post-compromise behavior.
  • If the triage identified malware, search the environment for additional compromised hosts.
  • Implement temporary network rules, procedures, and segmentation to contain the malware.
  • Stop suspicious processes.
  • Immediately block the identified indicators of compromise (IoCs).
  • Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
  • Remove and block malicious artifacts identified during triage.
  • Restrict PowerShell usage outside of IT and engineering business units using GPOs, AppLocker, Intune, or similar software.
  • 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 through 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).

Setupedit

The PowerShell Script Block Logging logging policy must be configured (Enable).

Steps to implement the logging policy with Advanced Audit Configuration:

Computer Configuration >
Administrative Templates >
Windows PowerShell >
Turn on PowerShell Script Block Logging (Enable)

Steps to implement the logging policy via registry:

reg add "hklm\SOFTWARE\Policies\Microsoft\Windows\PowerShell\ScriptBlockLogging" /v EnableScriptBlockLogging /t REG_DWORD /d 1

Rule queryedit

event.category:process and host.os.type:windows and
  powershell.file.script_block_text:(
    "Invoke-TokenManipulation" or
    "ImpersonateNamedPipeClient" or
    "NtImpersonateThread" or
    (
      "STARTUPINFOEX" and
      "UpdateProcThreadAttribute"
    ) or
    (
      "AdjustTokenPrivileges" and
      "SeDebugPrivilege"
    ) or
    (
      ("DuplicateToken" or
      "DuplicateTokenEx") and
      ("SetThreadToken" or
      "ImpersonateLoggedOnUser" or
      "CreateProcessWithTokenW" or
      "CreatePRocessAsUserW" or
      "CreateProcessAsUserA")
    )
  ) and
  not (
    user.id:("S-1-5-18" or "S-1-5-19" or "S-1-5-20") and
    file.directory: "C:\\ProgramData\\Microsoft\\Windows Defender Advanced Threat Protection\\Downloads"
  ) and
  not powershell.file.script_block_text : (
    "sentinelbreakpoints" and "Set-PSBreakpoint" and "PowerSploitIndicators"
  )

Framework: MITRE ATT&CKTM

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