Arbitrary File Download Via Squirrel.EXE

Hunt Hypothesis

Detects the usage of the “Squirrel.exe” to download arbitrary files. This binary is part of multiple Electron based software installations (Slack, Teams, Discord, etc.)

Detection Rule

Sigma (Original)

title: Arbitrary File Download Via Squirrel.EXE
id: 1e75c1cc-c5d4-42aa-ac3d-91b0b68b3b4c
related:
    - id: 45239e6a-b035-4aaf-b339-8ad379fcb67e
      type: similar
    - id: fa4b21c9-0057-4493-b289-2556416ae4d7
      type: obsolete
status: test
description: |
    Detects the usage of the "Squirrel.exe" to download arbitrary files. This binary is part of multiple Electron based software installations (Slack, Teams, Discord, etc.)
references:
    - https://lolbas-project.github.io/lolbas/OtherMSBinaries/Squirrel/
    - http://www.hexacorn.com/blog/2019/03/30/sqirrel-packages-manager-as-a-lolbin-a-k-a-many-electron-apps-are-lolbins-by-default/
    - http://www.hexacorn.com/blog/2018/08/16/squirrel-as-a-lolbin/
author: Nasreddine Bencherchali (Nextron Systems), Karneades / Markus Neis, Jonhnathan Ribeiro, oscd.community
date: 2022-06-09
modified: 2023-11-09
tags:
    - attack.execution
    - attack.stealth
    - attack.t1218
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        Image|endswith:
            - '\squirrel.exe'
            - '\update.exe'
    selection_download_cli:
        CommandLine|contains:
            - ' --download '
            - ' --update '
            - ' --updateRollback='
    selection_download_http_keyword:
        CommandLine|contains: 'http'
    condition: all of selection_*
falsepositives:
    - Expected FP with some Electron based applications such as (1Clipboard, Beaker Browser, Caret, Discord, GitHub Desktop, etc.)
level: medium

KQL (Azure Sentinel)

imProcessCreate
| where (TargetProcessName endswith "\\squirrel.exe" or TargetProcessName endswith "\\update.exe") and (TargetProcessCommandLine contains " --download " or TargetProcessCommandLine contains " --update " or TargetProcessCommandLine contains " --updateRollback=") and TargetProcessCommandLine contains "http"

Required Data Sources

False Positive Guidance

• Expected FP with some Electron based applications such as (1Clipboard, Beaker Browser, Caret, Discord, GitHub Desktop, etc.)

MITRE ATT&CK Context

• Tactic: Execution
• Technique: T1218 — T1218

References

• https://lolbas-project.github.io/lolbas/OtherMSBinaries/Squirrel/
• http://www.hexacorn.com/blog/2019/03/30/sqirrel-packages-manager-as-a-lolbin-a-k-a-many-electron-apps-are-lolbins-by-default/
• http://www.hexacorn.com/blog/2018/08/16/squirrel-as-a-lolbin/
• SigmaHQ Rule