[metadata]
creation_date = "2023/03/20"
integration = ["endpoint", "windows"]
maturity = "production"
min_stack_comments = "New fields added: required_fields, related_integrations, setup"
min_stack_version = "8.3.0"
updated_date = "2023/06/22"

[rule]
author = ["Elastic"]
description = """
Identifies execution of common Microsoft Office applications to launch an Office Add-In from a suspicious path or 
with an unusual parent process. This may indicate an attempt to get initial access via a malicious phishing 
MS Office Add-In.
"""
from = "now-9m"
index = ["winlogbeat-*", "logs-endpoint.events.*", "logs-windows.*", "endgame-*"]
language = "eql"
license = "Elastic License v2"
name = "Suspicious Execution via Microsoft Office Add-Ins"
references = [
"https://github.com/Octoberfest7/XLL_Phishing",
"https://labs.f-secure.com/archive/add-in-opportunities-for-office-persistence/"
]
risk_score = 47
rule_id = "ae8a142c-6a1d-4918-bea7-0b617e99ecfa"
severity = "medium"
tags = ["Domain: Endpoint", "OS: Windows", "Use Case: Threat Detection", "Tactic: Initial Access", "Tactic: Persistence", "Data Source: Elastic Endgame", "Data Source: Elastic Defend"]
timestamp_override = "event.ingested"
type = "eql"

query = '''
process where 
    
    host.os.type == "windows" and event.type == "start" and  
    
    process.name : ("WINWORD.EXE", "EXCEL.EXE", "POWERPNT.EXE", "MSACCESS.EXE", "VSTOInstaller.exe") and 
    
    process.args regex~ """.+\.(wll|xll|ppa|ppam|xla|xlam|vsto)""" and 
    
    /* Office Add-In from suspicious paths */
    (process.args :
             ("?:\\Users\\*\\Temp\\7z*",
              "?:\\Users\\*\\Temp\\Rar$*",
              "?:\\Users\\*\\Temp\\Temp?_*",
              "?:\\Users\\*\\Temp\\BNZ.*",
              "?:\\Users\\*\\Downloads\\*",
              "?:\\Users\\*\\AppData\\Roaming\\*",
              "?:\\Users\\Public\\*",
              "?:\\ProgramData\\*",
              "?:\\Windows\\Temp\\*",
              "\\Device\\*",
              "http*") or
	      
    process.parent.name : ("explorer.exe", "OpenWith.exe") or 
    
    /* Office Add-In from suspicious parent */
    process.parent.name : ("cmd.exe", "powershell.exe")) and
	  
    /* False Positives */
    not (process.args : "*.vsto" and
         process.parent.executable :
                   ("?:\\Program Files\\Logitech\\LogiOptions\\PlugInInstallerUtility*.exe",
                    "?:\\ProgramData\\Logishrd\\LogiOptions\\Plugins\\VSTO\\*\\VSTOInstaller.exe",
                    "?:\\Program Files\\Logitech\\LogiOptions\\PlugInInstallerUtility.exe",
                    "?:\\Program Files\\LogiOptionsPlus\\PlugInInstallerUtility*.exe",
                    "?:\\ProgramData\\Logishrd\\LogiOptionsPlus\\Plugins\\VSTO\\*\\VSTOInstaller.exe",
                    "?:\\Program Files\\Common Files\\microsoft shared\\VSTO\\*\\VSTOInstaller.exe")) and
    not (process.args : "/Uninstall" and process.name : "VSTOInstaller.exe") and
    not (process.parent.name : "rundll32.exe" and
         process.parent.args : "?:\\WINDOWS\\Installer\\MSI*.tmp,zzzzInvokeManagedCustomActionOutOfProc") and
    not (process.name : "VSTOInstaller.exe" and process.args : "https://dl.getsidekick.com/outlook/vsto/Sidekick.vsto")
'''


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



[[rule.threat]]
framework = "MITRE ATT&CK"
[[rule.threat.technique]]
id = "T1137"
name = "Office Application Startup"
reference = "https://attack.mitre.org/techniques/T1137/"
[[rule.threat.technique.subtechnique]]
id = "T1137.006"
name = "Add-ins"
reference = "https://attack.mitre.org/techniques/T1137/006/"
	
[rule.threat.tactic]
id = "TA0003"
name = "Persistence"
reference = "https://attack.mitre.org/tactics/TA0003/"