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Detection rules › Sigma

Invoke-Obfuscation VAR++ LAUNCHER OBFUSCATION

Status
test
Severity
high
Log source
product windows, category process_creation
Author
Timur Zinniatullin, oscd.community
Source
github.com/SigmaHQ/sigma

Detects Obfuscated Powershell via VAR++ LAUNCHER

MITRE ATT&CK coverage

TacticTechniques
ExecutionT1059.001 Command and Scripting Interpreter: PowerShell
StealthT1027 Obfuscated Files or Information

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation
Security-AuditingEvent ID 4688A new process has been created.

Rule body yaml

title: Invoke-Obfuscation VAR++ LAUNCHER OBFUSCATION
id: e9f55347-2928-4c06-88e5-1a7f8169942e
status: test
description: Detects Obfuscated Powershell via VAR++ LAUNCHER
references:
    - https://github.com/SigmaHQ/sigma/issues/1009 # (Task27)
author: Timur Zinniatullin, oscd.community
date: 2020-10-13
modified: 2022-11-16
tags:
    - attack.stealth
    - attack.t1027
    - attack.execution
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        # CommandLine|re: '(?i)&&set.*(\{\d\}){2,}\\\"\s+?\-f.*&&.*cmd.*\/c' # FPs with |\/r
        # Example 1: CMD /C"sET KUR=Invoke-Expression (New-Object Net.WebClient).DownloadString&&Set MxI=C:\wINDowS\sYsWow64\winDOWspoWERSheLl\V1.0\PowerShelL.EXe ${ExEcut`IoN`cON`TExT}.\"invo`kEcoMm`A`ND\".( \"{2}{1}{0}\" -f 'pt','EscRi','INvOk' ).Invoke( ( .( \"{0}{1}\" -f'D','IR' ) ( \"{0}{1}\"-f'ENV:kU','R')).\"vAl`Ue\" )&& CMD /C%mXI%"
        # Example 2: c:\WiNDOWS\sYSTEm32\CmD.exE /C "sEt DeJLz=Invoke-Expression (New-Object Net.WebClient).DownloadString&&set yBKM=PoWERShelL -noeX ^^^&(\"{2}{0}{1}\"-f '-ItE','m','seT') ( 'V' + 'a'+ 'RiAblE:z8J' +'U2' + 'l' ) ([TYpE]( \"{2}{3}{0}{1}\"-f 'e','NT','e','NViRONM' ) ) ; ^^^& ( ( [sTrIng]${VE`Rbo`SepReFER`Ence})[1,3] + 'X'-joIN'')( ( (.('gI') ('V' + 'a' + 'RIAbLe:z8j' + 'u2' +'l' ) ).vALUe::( \"{2}{5}{0}{1}{6}{4}{3}\" -f 'IRo','Nm','GETE','ABlE','I','nv','enTVAr').Invoke(( \"{0}{1}\"-f'd','ejLz' ),( \"{1}{2}{0}\"-f'cEss','P','RO') )) )&& c:\WiNDOWS\sYSTEm32\CmD.exE /C %ybkm%"
        CommandLine|contains|all:
            - '&&set'
            - 'cmd'
            - '/c'
            - '-f'
        CommandLine|contains:
            - '{0}'
            - '{1}'
            - '{2}'
            - '{3}'
            - '{4}'
            - '{5}'
    condition: selection
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: condition

selection

Stage 1: selection

selection:
    CommandLine|contains|all:
        - '&&set'
        - 'cmd'
        - '/c'
        - '-f'
    CommandLine|contains:
        - '{0}'
        - '{1}'
        - '{2}'
        - '{3}'
        - '{4}'
        - '{5}'

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
  • &&set
  • -f corpus 9 (sigma 7, splunk 2)
  • /c corpus 15 (sigma 13, splunk 2)
  • cmd corpus 8 (sigma 8)
  • {0}
  • {1}
  • {2}
  • {3}
  • {4}
  • {5}