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Bypass UAC via Event Viewer

Elastic Stack Serverless Security

Identifies User Account Control (UAC) bypass via eventvwr.exe. Attackers bypass UAC to stealthily execute code with elevated permissions.

Rule type: eql

Rule indices:

  • winlogbeat-*
  • logs-endpoint.events.*
  • logs-windows.*

Severity: high

Risk score: 73

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
  • Privilege Escalation
  • Investigation Guide

Version: 102

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

Windows User Account Control (UAC) allows a program to elevate its privileges (tracked as low to high integrity levels)
to perform a task under administrator-level permissions, possibly by prompting the user for confirmation.
UAC can deny an operation under high-integrity enforcement, or allow the user to perform the action if they are in the
local administrators group and enter an administrator password when prompted.

For more information about the UAC and how it works, check the official Microsoft docs page.

During startup, eventvwr.exe checks the registry value of the HKCU\Software\Classes\mscfile\shell\open\command
registry key for the location of mmc.exe, which is used to open the eventvwr.msc saved console file. If the location
of another binary or script is added to this registry value, it will be executed as a high-integrity process without a
UAC prompt being displayed to the user. This rule detects this UAC bypass by monitoring processes spawned by
eventvwr.exe other than mmc.exe and werfault.exe.

Note:
This investigation guide uses the Osquery Markdown Plugin introduced in Elastic stack version 8.5.0. Older Elastic stacks versions will see unrendered markdown in this guide.

  • 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.
  • Inspect the host for suspicious or abnormal behavior in the alert timeframe.
  • Investigate any abnormal behavior by the subject process such as network connections, registry or file modifications,
    and any spawned child processes.
  • Examine the host for derived artifacts that indicates suspicious activities:
    • Analyze the process executable 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{"query":"SELECT * FROM dns_cache", "label":"Osquery - Retrieve 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{"query":"SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services","label":"Osquery - Retrieve All Services"}}
        • !{osquery{"query":"SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services WHERE NOT (user_account LIKE "%LocalSystem" OR user_account LIKE "%LocalService" OR user_account LIKE "%NetworkService" OR user_account == null)","label":"Osquery - Retrieve Services Running on User Accounts"}}
        • !{osquery{"query":"SELECT concat('https://www.virustotal.com/gui/file/', sha1) AS VtLink, name, description, start_type, status, pid, services.path FROM services JOIN authenticode ON services.path = authenticode.path OR services.module_path = authenticode.path JOIN hash ON services.path = hash.path WHERE authenticode.result != "trusted"","label":"Osquery - Retrieve Service Unsigned Executables with Virustotal Link"}}
    • 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.
  • This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.
  • Initiate the incident response process based on the outcome of the triage.
  • Isolate the involved host 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.
  • Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and
    malware components.
  • 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.
  • 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).

Rule query

process where event.type == "start" and
  process.parent.name : "eventvwr.exe" and
  not process.executable :
            ("?:\\Windows\\SysWOW64\\mmc.exe",
             "?:\\Windows\\System32\\mmc.exe",
             "?:\\Windows\\SysWOW64\\WerFault.exe",
             "?:\\Windows\\System32\\WerFault.exe")

Framework: MITRE ATT&CKTM