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Detection rules › Sigma

Process Access via TrolleyExpress Exclusion

Status
test
Severity
high
Log source
product windows, category process_creation
Author
Florian Roth (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects a possible process memory dump that uses the white-listed Citrix TrolleyExpress.exe filename as a way to dump the lsass process memory

MITRE ATT&CK coverage

TacticTechniques
StealthT1218.011 System Binary Proxy Execution: Rundll32
Credential AccessT1003.001 OS Credential Dumping: LSASS Memory

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation

Rule body yaml

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

Stages and Predicates

Stage 0: condition

selection or ( renamed and not 1 of filter* )

Stage 1: selection

selection:
    CommandLine|contains:
        - '\TrolleyExpress 7'
        - '\TrolleyExpress 8'
        - '\TrolleyExpress 9'
        - '\TrolleyExpress.exe 7'
        - '\TrolleyExpress.exe 8'
        - '\TrolleyExpress.exe 9'
        - '\TrolleyExpress.exe -ma '

Stage 2: renamed

renamed:
    Image|endswith: '\TrolleyExpress.exe'

Stage 3: not filter*

filter_renamed:
    OriginalFileName|contains: 'CtxInstall'
filter_empty:
    OriginalFileName: null

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

FieldKindExcluded values
OriginalFileNameis_null(no value, null check)
OriginalFileNamematchCtxInstall

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
CommandLinematch
  • \TrolleyExpress 7
  • \TrolleyExpress 8
  • \TrolleyExpress 9
  • \TrolleyExpress.exe -ma
  • \TrolleyExpress.exe 7
  • \TrolleyExpress.exe 8
  • \TrolleyExpress.exe 9
Imageends_with
  • \TrolleyExpress.exe corpus 2 (sigma 2)