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Detection rules › Sigma

Qakbot Rundll32 Fake DLL Extension Execution

Status
test
Severity
critical
Log source
product windows, category process_creation
Author
X__Junior (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects specific process tree behavior of a "rundll32" execution where the DLL doesn't have the ".dll" extension. This is often linked with potential Qakbot activity.

MITRE ATT&CK coverage

TacticTechniques
ExecutionNo specific technique
StealthNo specific technique

Event coverage

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

Rule body yaml

title: Qakbot Rundll32 Fake DLL Extension Execution
id: bfd34392-c591-4009-b938-9fd985a28b85
status: test
description: Detects specific process tree behavior of a "rundll32" execution where the DLL doesn't have the ".dll" extension. This is often linked with potential Qakbot activity.
references:
    - https://github.com/pr0xylife/Qakbot/
author: X__Junior (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
date: 2023-05-24
tags:
    - attack.execution
    - detection.emerging-threats
    - attack.stealth
logsource:
    product: windows
    category: process_creation
detection:
    selection:
        ParentImage|endswith:
            # Note: Only add processes seen used by Qakbot to avoid collision with other strains of malware
            - '\cmd.exe'
            - '\cscript.exe'
            - '\curl.exe'
            - '\mshta.exe'
            - '\powershell.exe'
            - '\pwsh.exe'
            - '\wscript.exe'
        Image|endswith: '\rundll32.exe'
        CommandLine|contains:
            # Note: Only add paths seen used by Qakbot to avoid collision with other strains of malware
            - ':\ProgramData\'
            - ':\Users\Public\'
            - '\AppData\Local\Temp\'
            - '\AppData\Roaming\'
    filter_main_extension:
        CommandLine|contains: '.dll'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unlikely
level: critical

Stages and Predicates

Stage 0: condition

selection and not 1 of filter_main_*

Stage 1: selection

selection:
    ParentImage|endswith:
        - '\cmd.exe'
        - '\cscript.exe'
        - '\curl.exe'
        - '\mshta.exe'
        - '\powershell.exe'
        - '\pwsh.exe'
        - '\wscript.exe'
    Image|endswith: '\rundll32.exe'
    CommandLine|contains:
        - ':\ProgramData\'
        - ':\Users\Public\'
        - '\AppData\Local\Temp\'
        - '\AppData\Roaming\'

Stage 2: not filter_main_extension

filter_main_extension:
    CommandLine|contains: '.dll'

Exclusions

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

FieldKindExcluded values
CommandLinematch.dll

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
  • :\ProgramData\ corpus 9 (sigma 9)
  • :\Users\Public\ corpus 18 (sigma 18)
  • \AppData\Local\Temp\ corpus 26 (sigma 26)
  • \AppData\Roaming\ corpus 16 (sigma 16)
Imageends_with
  • \rundll32.exe corpus 95 (sigma 95)
ParentImageends_with
  • \cmd.exe corpus 20 (sigma 20)
  • \cscript.exe corpus 17 (sigma 17)
  • \curl.exe corpus 3 (sigma 3)
  • \mshta.exe corpus 13 (sigma 13)
  • \powershell.exe corpus 24 (sigma 24)
  • \pwsh.exe corpus 21 (sigma 21)
  • \wscript.exe corpus 19 (sigma 19)