Potential Pikabot Hollowing Activity

Status: test
Severity: high
Log source: category process_creation, product windows
Author: Andreas Braathen (mnemonic.io)
Source: github.com/SigmaHQ/sigma

Detects the execution of rundll32 that leads to the invocation of legitimate Windows binaries. The malware Pikabot has been seen to use this technique for process hollowing through hard-coded Windows binaries

Known false positives

Unlikely

MITRE ATT&CK coverage

Tactic	Techniques
Privilege Escalation	`T1055.012` Process Injection: Process Hollowing
Stealth	`T1055.012` Process Injection: Process Hollowing

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: Potential Pikabot Hollowing Activity
id: d8937fe7-42d5-4b4d-8178-e089c908f63f
status: test
description: |
    Detects the execution of rundll32 that leads to the invocation of legitimate Windows binaries.
    The malware Pikabot has been seen to use this technique for process hollowing through hard-coded Windows binaries
references:
    - https://www.virustotal.com/gui/file/b6e8910fb9b3bb1fcddefd35ff0ed8624930d30d6977e11808c8330415685a62
    - https://www.virustotal.com/gui/file/6bb4cdbaef03b732a93559a58173e7f16b29bfb159a1065fae9185000ff23b4b
    - https://github.com/pr0xylife/Pikabot/blob/7f7723a74ca325ec54c6e61e076acce9a4b20538/Pikabot_06.12.2023.txt
author: Andreas Braathen (mnemonic.io)
date: 2023-10-27
modified: 2024-01-26
tags:
    - attack.privilege-escalation
    - attack.stealth
    - attack.t1055.012
    - detection.emerging-threats
logsource:
    product: windows
    category: process_creation
detection:
    selection:
        ParentImage|endswith: '\rundll32.exe'
        Image|endswith:
            # Note: Only add processes seen used by Pikabot to avoid collision with other strains of malware
            - '\SearchFilterHost.exe'
            - '\SearchProtocolHost.exe'
            - '\sndvol.exe'
            - '\wermgr.exe'
            - '\wwahost.exe'
    filter_main_legit_sndvol:
        Image|endswith: '\sndvol.exe'
        ParentCommandLine|contains: 'mmsys.cpl'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unlikely
level: high

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    ParentImage|endswith: '\rundll32.exe'
    Image|endswith:
        - '\SearchFilterHost.exe'
        - '\SearchProtocolHost.exe'
        - '\sndvol.exe'
        - '\wermgr.exe'
        - '\wwahost.exe'

Stage 2: `not filter_main_legit_sndvol`

filter_main_legit_sndvol:
    Image|endswith: '\sndvol.exe'
    ParentCommandLine|contains: 'mmsys.cpl'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Image`	ends_with	`\sndvol.exe`	`excludes:Image` `field:"Image" value:"\sndvol.exe"`
`ParentCommandLine`	match	`mmsys.cpl`	`excludes:ParentCommandLine` `field:"ParentCommandLine" value:"mmsys.cpl"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Image`	ends_with	`\SearchFilterHost.exe` corpus 3 (sigma 3) `\SearchProtocolHost.exe` corpus 2 (sigma 2) `\sndvol.exe` corpus 2 (sigma 2) `\wermgr.exe` corpus 5 (sigma 5) `\wwahost.exe` corpus 2 (sigma 2)	`field:"Image" kind:ends_with`
`ParentImage`	ends_with	`\rundll32.exe` corpus 15 (sigma 15)	`field:"ParentImage" kind:ends_with value:"\rundll32.exe"`