Dllhost.EXE Execution Anomaly

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

Detects a "dllhost" process spawning with no commandline arguments which is very rare to happen and could indicate process injection activity or malware mimicking similar system processes.

Known false positives

Unlikely

MITRE ATT&CK coverage

Tactic	Techniques
Privilege Escalation	`T1055` Process Injection
Stealth	`T1055` Process Injection

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: Dllhost.EXE Execution Anomaly
id: e7888eb1-13b0-4616-bd99-4bc0c2b054b9
status: test
description: Detects a "dllhost" process spawning with no commandline arguments which is very rare to happen and could indicate process injection activity or malware mimicking similar system processes.
references:
    - https://redcanary.com/blog/child-processes/
    - https://nasbench.medium.com/what-is-the-dllhost-exe-process-actually-running-ef9fe4c19c08
    - https://www.ncsc.gov.uk/static-assets/documents/malware-analysis-reports/goofy-guineapig/NCSC-MAR-Goofy-Guineapig.pdf
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-06-27
modified: 2023-05-15
tags:
    - attack.privilege-escalation
    - attack.stealth
    - attack.t1055
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\dllhost.exe'
        CommandLine:
            - 'dllhost.exe'
            - 'dllhost'
    filter_main_null:
        CommandLine: null
    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:
    Image|endswith: '\dllhost.exe'
    CommandLine:
        - 'dllhost.exe'
        - 'dllhost'

Stage 2: `not filter_main_null`

filter_main_null:
    CommandLine: null

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`CommandLine`	is_null	(no value, null check)	`excludes:CommandLine`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	eq	`dllhost` `dllhost.exe`	`field:"CommandLine" kind:eq`
`Image`	ends_with	`\dllhost.exe` corpus 11 (sigma 11)	`field:"Image" kind:ends_with value:"\dllhost.exe"`