Suspicious Binary In User Directory Spawned From Office Application

Status: test
Severity: high
Log source: category process_creation, product windows
Author: Jason Lynch
Source: github.com/SigmaHQ/sigma

Detects an executable in the users directory started from one of the Microsoft Office suite applications (Word, Excel, PowerPoint, Publisher, Visio)

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1204.002` User Execution: Malicious File

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: Suspicious Binary In User Directory Spawned From Office Application
id: aa3a6f94-890e-4e22-b634-ffdfd54792cc
status: test
description: Detects an executable in the users directory started from one of the Microsoft Office suite applications (Word, Excel, PowerPoint, Publisher, Visio)
references:
    - https://blog.morphisec.com/fin7-not-finished-morphisec-spots-new-campaign
    - https://www.virustotal.com/gui/file/23160972c6ae07f740800fa28e421a81d7c0ca5d5cab95bc082b4a986fbac57
author: Jason Lynch
date: 2019-04-02
modified: 2023-02-04
tags:
    - attack.execution
    - attack.t1204.002
    - attack.g0046
    - car.2013-05-002
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        ParentImage|endswith:
            - '\WINWORD.EXE'
            - '\EXCEL.EXE'
            - '\POWERPNT.exe'
            - '\MSPUB.exe'
            - '\VISIO.exe'
            - '\MSACCESS.exe'
            - '\EQNEDT32.exe'
            # - '\OUTLOOK.EXE' too many FPs
        Image|startswith: 'C:\users\'
        Image|endswith: '.exe'
    filter:
        Image|endswith: '\Teams.exe'
    condition: selection and not filter
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    ParentImage|endswith:
        - '\WINWORD.EXE'
        - '\EXCEL.EXE'
        - '\POWERPNT.exe'
        - '\MSPUB.exe'
        - '\VISIO.exe'
        - '\MSACCESS.exe'
        - '\EQNEDT32.exe'
    Image|startswith: 'C:\users\'
    Image|endswith: '.exe'

Stage 2: `not filter`

filter:
    Image|endswith: '\Teams.exe'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Image`	ends_with	`\Teams.exe`	`excludes:Image` `field:"Image" value:"\Teams.exe"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Image`	ends_with	`.exe` corpus 4 (sigma 4)	`field:"Image" kind:ends_with value:".exe"`
`Image`	starts_with	`C:\users\` corpus 2 (sigma 1, elastic 1)	`field:"Image" kind:starts_with value:"C:\users\"`
`ParentImage`	ends_with	`\EQNEDT32.exe` corpus 5 (sigma 5) `\EXCEL.EXE` corpus 8 (sigma 8) `\MSACCESS.exe` corpus 4 (sigma 4) `\MSPUB.exe` corpus 4 (sigma 4) `\POWERPNT.exe` corpus 6 (sigma 6) `\VISIO.exe` corpus 4 (sigma 4) `\WINWORD.EXE` corpus 10 (sigma 10)	`field:"ParentImage" kind:ends_with`