DLL Concatenation (Windows Event Log)

id: '33834.59905'
title: DLL Concatenation
description: 'Threat actors were observed using Impacket to concatenate the malicious
  proxy tool Stowaway (msoe.dll) with all DLLs starting with ''d'' from the system32
  directory into a single DLL (appmgmt.dll) to pad and obfuscate the malicious DLL,
  thereby facilitating its deployment and evasion. This use case detects copy commands
  followed by either *.dll or multiple .dll references, indicating possible attempts
  to concatenate multiple DLLs into a single file. NOTE: For commands using ''copy''
  or ''type'', they must be executed in a way that creates a new process, e.g. with
  cmd /c or powershell -c, as they are built-in commands that run within the current
  cmd session and do not create new processes on their own.'
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_winevent` (TERM(EventCode=4688) OR
  "<EventID>4688<" OR Type=Process) (TERM(copy) OR TERM(robocopy) OR TERM(xcopy) OR
  ((TERM(type) OR TERM(Get-Content) OR "gc" OR "cat" OR TERM(more)) ">")) ".dll" |
  regex process="(?i)(copy|more|Get-Content|type|cat|gc)\s+.*?((\/b\s+\S+\.dll\s+\+\s*\S+\.dll)|(\*\.dll\s+\S+)|(\.dll.*\.dll))"|
  table _time, host, user, process, process_*, parent_* | bin span=1s | stats values(*)
  as * by _time, host '
techniques:
- defense-evasion:masquerading
- defense-evasion:obfuscated files or information:binary padding
technique_id:
- T1036
- T1027.001
data_category:
- Process command-line parameters
- Windows event logs
references:
- https://attack.mitre.org/techniques/T1027/001/
- https://news.sophos.com/en-us/2024/06/05/operation-crimson-palace-a-technical-deep-dive/