Suspicious Outlook Child Process

[metadata]
bypass_bbr_timing = true
creation_date = "2025/01/10"
integration = ["endpoint"]
maturity = "production"
updated_date = "2026/03/24"

[rule]
author = ["Elastic"]
building_block_type = "default"
description = """
Identifies suspicious child processes spawned by MS Outlook, which can indicate a potential masquerading or the
exploitation of a vulnerability on the application causing it to execute code.
"""
from = "now-9m"
index = ["logs-endpoint.events.process-*"]
language = "eql"
license = "Elastic License v2"
name = "Suspicious Outlook Child Process"
risk_score = 21
rule_id = "6cf17149-a8e3-44ec-9ec9-fdc8535547a1"
severity = "low"
tags = [
    "Domain: Endpoint",
    "OS: Windows",
    "Use Case: Threat Detection",
    "Tactic: Defense Evasion",
    "Tactic: Persistence",
    "Rule Type: BBR",
    "Data Source: Elastic Defend",
]
timestamp_override = "event.ingested"
type = "eql"

query = '''
process where host.os.type == "windows" and event.type == "start" and
  process.parent.name : "outlook.exe" and
  not (
    (
      process.executable : (
        "?:\\Program Files\\*",
        "?:\\Program Files (x86)\\*",
        "?:\\Windows\\System32\\WerFault.exe",
        "?:\\Windows\\SysWOW64\\WerFault.exe",
        "?:\\Windows\\system32\\wermgr.exe",
        "?:\\Users\\*\\AppData\\Local\\Microsoft\\Teams\\current\\Teams.exe",
        "?:\\Users\\*\\AppData\\Local\\Temp\\NewOutlookInstall\\NewOutlookInstaller.exe",
        "?:\\Users\\*\\AppData\\Local\\Google\\Chrome\\Application\\chrome.exe",
        "?:\\Users\\*\\AppData\\Local\\Island\\Island\\Application\\Island.exe",
        "?:\\Users\\*\\AppData\\Local\\Mozilla Firefox\\firefox.exe",
        "?:\\Users\\*\\AppData\\Roaming\\Zoom\\bin\\Zoom.exe",
        "?:\\Windows\\System32\\IME\\SHARED\\IMEWDBLD.EXE",
        "?:\\Windows\\System32\\spool\\drivers\\x64\\*",
        "?:\\Windows\\System32\\prevhost.exe",
        "?:\\Windows\\System32\\dwwin.exe",
        "?:\\Windows\\System32\\mspaint.exe",
        "?:\\Windows\\SysWOW64\\mspaint.exe",
        "?:\\Windows\\System32\\notepad.exe",
        "?:\\Windows\\SysWOW64\\notepad.exe",
        "?:\\Windows\\System32\\smartscreen.exe",
        "?:\\Windows\\explorer.exe",
        "?:\\Windows\\splwow64.exe"
      ) and process.code_signature.trusted == true  
    ) or
    (
      process.name : "rundll32.exe" and
      process.args : "*hpmsn???.dll,MonitorPrintJobStatus*"
    )
  )
'''


[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1036"
name = "Masquerading"
reference = "https://attack.mitre.org/techniques/T1036/"

[[rule.threat.technique.subtechnique]]
id = "T1036.001"
name = "Invalid Code Signature"
reference = "https://attack.mitre.org/techniques/T1036/001/"

[[rule.threat.technique.subtechnique]]
id = "T1036.005"
name = "Match Legitimate Resource Name or Location"
reference = "https://attack.mitre.org/techniques/T1036/005/"

[[rule.threat.technique]]
id = "T1055"
name = "Process Injection"
reference = "https://attack.mitre.org/techniques/T1055/"

[rule.threat.tactic]
id = "TA0005"
name = "Defense Evasion"
reference = "https://attack.mitre.org/tactics/TA0005/"

[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1554"
name = "Compromise Host Software Binary"
reference = "https://attack.mitre.org/techniques/T1554/"

[rule.threat.tactic]
id = "TA0003"
name = "Persistence"
reference = "https://attack.mitre.org/tactics/TA0003/"

[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1203"
name = "Exploitation for Client Execution"
reference = "https://attack.mitre.org/techniques/T1203/"

[rule.threat.tactic]
id = "TA0002"
name = "Execution"
reference = "https://attack.mitre.org/tactics/TA0002/"