Windows ZxShell activity via rundll32.exe using zxFunction and RemoteDiskXXXXX

title: Windows ZxShell activity via rundll32.exe using zxFunction and RemoteDiskXXXXX
id: ac06fea2-6723-4e17-a16c-4c26b175b1a5
status: test
description: This rule flags process creation events where rundll32.exe is launched and the command line contains the strings zxFunction and RemoteDiskXXXXX. Matching these well-known function and disk-naming indicators helps identify ZxShell staging behavior and related execution attempts. It relies on Windows process creation telemetry with access to the image path and the full command line.
references:
  - https://www.hybrid-analysis.com/sample/5d2a4cde9fa7c2fdbf39b2e2ffd23378d0c50701a3095d1e91e3cf922d7b0b16?environmentId=100
  - https://pub-7cb8ac806c1b4c4383e585c474a24719.r2.dev/116309e7121bc8b0e66e4166c06f7b818e1d3629.pdf
  - https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2014/TA/Axiom/proc_creation_win_apt_zxshell.yml
author: Florian Roth (Nextron Systems), oscd.community, Jonhnathan Ribeiro, Huntrule Team
date: 2017-07-20
modified: 2021-11-27
tags:
  - attack.execution
  - attack.stealth
  - attack.t1059.003
  - attack.t1218.011
  - attack.s0412
  - attack.g0001
  - detection.emerging-threats
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    Image|endswith: \rundll32.exe
    CommandLine|contains:
      - zxFunction
      - RemoteDiskXXXXX
  condition: selection
falsepositives:
  - Unlikely
level: critical
license: DRL-1.1
related:
  - id: f0b70adb-0075-43b0-9745-e82a1c608fcc
    type: derived