Process Access via TrolleyExpress Exclusion — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems). Source status: test; severity: high. Source dates: 2022-02-10 / 2022-05-13.

{
  "category": "process_creation",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 736ddd3ccc7cc6ae1056837a36c5e59c9c282782cc081ff31431d87e7fb2ba31

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Process Access via TrolleyExpress Exclusion
id: 4c0aaedc-154c-4427-ada0-d80ef9c9deb6
status: test
description: Detects a possible process memory dump that uses the white-listed Citrix TrolleyExpress.exe filename as a way to dump the lsass process memory
references:
    - https://twitter.com/_xpn_/status/1491557187168178176
    - https://www.youtube.com/watch?v=Ie831jF0bb0
author: Florian Roth (Nextron Systems)
date: 2022-02-10
modified: 2022-05-13
tags:
    - attack.stealth
    - attack.t1218.011
    - attack.credential-access
    - attack.t1003.001
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        CommandLine|contains:
      # We assume that the lsass.exe process has a process ID that's between 700 and 999 and the dumper uses just the PID as parameter
            - '\TrolleyExpress 7'
            - '\TrolleyExpress 8'
            - '\TrolleyExpress 9'
            - '\TrolleyExpress.exe 7'
            - '\TrolleyExpress.exe 8'
            - '\TrolleyExpress.exe 9'
      # Common dumpers
            - '\TrolleyExpress.exe -ma '
    renamed:
        Image|endswith: '\TrolleyExpress.exe'
    filter_renamed:
        OriginalFileName|contains: 'CtxInstall'
    filter_empty:
        OriginalFileName: null
    condition: selection or ( renamed and not 1 of filter* )
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://twitter.com/_xpn_/status/1491557187168178176
• https://www.youtube.com/watch?v=Ie831jF0bb0