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Suspicious Execution via Microsoft Office Add-Ins

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Suspicious Execution via Microsoft Office Add-Ins

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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.

Rule type: eql

Rule indices:

winlogbeat-*
logs-endpoint.events.*
logs-windows.sysmon_operational-*
endgame-*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

Domain: Endpoint
OS: Windows
Use Case: Threat Detection
Tactic: Initial Access
Tactic: Persistence
Data Source: Elastic Endgame
Data Source: Elastic Defend
Data Source: Sysmon

Version: 4

Rule authors:

Elastic

Rule license: Elastic License v2

Rule query

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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")

Framework: MITRE ATT&CK^TM

Tactic:
- Name: Initial Access
- ID: TA0001
- Reference URL: https://attack.mitre.org/tactics/TA0001/
Technique:
- Name: Phishing
- ID: T1566
- Reference URL: https://attack.mitre.org/techniques/T1566/
Sub-technique:
- Name: Spearphishing Attachment
- ID: T1566.001
- Reference URL: https://attack.mitre.org/techniques/T1566/001/
Tactic:
- Name: Persistence
- ID: TA0003
- Reference URL: https://attack.mitre.org/tactics/TA0003/
Technique:
- Name: Office Application Startup
- ID: T1137
- Reference URL: https://attack.mitre.org/techniques/T1137/
Sub-technique:
- Name: Add-ins
- ID: T1137.006
- Reference URL: https://attack.mitre.org/techniques/T1137/006/

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