Windows Browser Process Launched with Unusual Flags

name: Windows Browser Process Launched with Unusual Flags
id: 841e2abc-0442-4e7f-b445-b22680632a08
version: 2
date: '2026-03-10'
author: Teoderick Contreras, Splunk
status: production
type: Anomaly
description: The following analytic detects the use of unusual browser flags, specifically --mute-audio and --do-not-elevate, which deviate from standard browser launch behavior. These flags may indicate automated scripts, testing environments, or attempts to modify browser functionality for silent operation or restricted privilege execution. Detection focuses on non-standard launch parameters, unexpected process behavior, or deviations from baseline configurations. Monitoring such flag usage helps identify potentially suspicious activity, misconfigurations, or policy violations, enabling security teams to investigate anomalies, ensure system compliance, and differentiate legitimate administrative or testing uses from unusual or unauthorized operations.
data_source:
    - Sysmon EventID 1
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where NOT (Processes.parent_process_name IN ("chrome.exe", "msedge.exe", "brave.exe", "firefox.exe", "explorer.exe")) AND NOT (Processes.parent_process_path IN("C:\\Program Files*", "C:\\Windows\\System32\\*", "C:\\Windows\\SysWow64\\*",)) AND Processes.process_name IN ("chrome.exe", "msedge.exe", "brave.exe", "firefox.exe") AND Processes.process IN ("*--mute-audio*","*--no-de-elevate*", "*--do-not-de-elevate*") by Processes.action Processes.dest Processes.original_file_name Processes.parent_process Processes.parent_process_exec Processes.parent_process_guid Processes.parent_process_id Processes.parent_process_name Processes.parent_process_path Processes.process Processes.process_exec Processes.process_guid Processes.process_hash Processes.process_id Processes.process_integrity_level Processes.process_name Processes.process_path Processes.user Processes.user_id Processes.vendor_product | `drop_dm_object_name(Processes)` | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `windows_browser_process_launched_with_unusual_flags_filter`'
how_to_implement: The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint` data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.
known_false_positives: It is possible false positives will be present based on third party applications. Filtering may be needed.
references:
    - https://www.recordedfuture.com/research/from-castleloader-to-castlerat-tag-150-advances-operations
    - https://peter.sh/experiments/chromium-command-line-switches/
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search dest="$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") starthoursago=168  | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
rba:
    message: chromium browser that has unusual flags for muting or audio and prevent de-elevation of the current process in $dest$.
    risk_objects:
        - field: dest
          type: system
          score: 20
    threat_objects:
        - field: parent_process_name
          type: parent_process_name
tags:
    analytic_story:
        - Castle RAT
    asset_type: Endpoint
    mitre_attack_id:
        - T1185
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1185/browser_unusual_flag/castle_chrome_shell32.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog