File with Suspicious Extension Downloaded

[metadata]
creation_date = "2023/09/27"
integration = ["endpoint"]
maturity = "production"
updated_date = "2026/03/24"

[rule]
author = ["Elastic"]
building_block_type = "default"
description = """
Identifies unusual files downloaded from outside the local network that have the potential to be abused for code
execution.
"""
from = "now-119m"
index = ["logs-endpoint.events.file-*"]
interval = "60m"
language = "eql"
license = "Elastic License v2"
name = "File with Suspicious Extension Downloaded"
references = [
    "https://x.com/Laughing_Mantis/status/1518766501385318406",
    "https://wikileaks.org/ciav7p1/cms/page_13763375.html",
]
risk_score = 21
rule_id = "8d366588-cbd6-43ba-95b4-0971c3f906e5"
severity = "low"
tags = [
    "Domain: Endpoint",
    "OS: Windows",
    "Use Case: Threat Detection",
    "Tactic: Defense Evasion",
    "Data Source: Elastic Defend",
    "Rule Type: BBR",
]
timestamp_override = "event.ingested"
type = "eql"

query = '''
file where host.os.type == "windows" and event.type == "creation" and
  file.extension : (
    "appinstaller", "application", "appx", "appxbundle", "cpl", "diagcab", "diagpkg", "diagcfg", "manifest",
    "msix", "pif", "search-ms", "searchConnector-ms", "settingcontent-ms", "symlink", "theme", "themepack" 
  ) and file.Ext.windows.zone_identifier > 1 and
  not
  (
    (
      file.extension : "msix" and 
      file.path : (
        "?:\\Users\\*\\AppData\\Local\\Temp\\WinGet\\Microsoft.Winget.Source*",
        "?:\\Windows\\system32\\config\\systemprofile\\AppData\\Local\\Microsoft\\WinGet\\State\\defaultState\\Microsoft.PreIndexed.Package\\Microsoft.Winget.Source*"
      )
    ) or
    (
      process.name : "Teams.exe" and process.code_signature.trusted == true and
      file.extension : "msix" and 
      file.path : "?:\\Users\\*\\AppData\\Roaming\\Microsoft\\Teams\\tmp\\*"
    )
  )
'''


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

[[rule.threat.technique]]
id = "T1218"
name = "System Binary Proxy Execution"
reference = "https://attack.mitre.org/techniques/T1218/"

[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 = "T1566"
name = "Phishing"
reference = "https://attack.mitre.org/techniques/T1566/"

[[rule.threat.technique.subtechnique]]
id = "T1566.001"
name = "Spearphishing Attachment"
reference = "https://attack.mitre.org/techniques/T1566/001/"

[[rule.threat.technique.subtechnique]]
id = "T1566.002"
name = "Spearphishing Link"
reference = "https://attack.mitre.org/techniques/T1566/002/"

[rule.threat.tactic]
id = "TA0001"
name = "Initial Access"
reference = "https://attack.mitre.org/tactics/TA0001/"

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

[[rule.threat.technique]]
id = "T1204"
name = "User Execution"
reference = "https://attack.mitre.org/techniques/T1204/"

[[rule.threat.technique.subtechnique]]
id = "T1204.002"
name = "Malicious File"
reference = "https://attack.mitre.org/techniques/T1204/002/"

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