Suspect Svchost Activity

Status: test
Severity: high
Log source: category process_creation, product windows
Author: David Burkett, @signalblur
Source: github.com/SigmaHQ/sigma

It is extremely abnormal for svchost.exe to spawn without any CLI arguments and is normally observed when a malicious process spawns the process and injects code into the process memory space.

Known false positives

Rpcnet.exe / rpcnetp.exe which is a lojack style software. https://www.blackhat.com/docs/us-14/materials/us-14-Kamlyuk-Kamluk-Computrace-Backdoor-Revisited.pdf

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: Suspect Svchost Activity
id: 16c37b52-b141-42a5-a3ea-bbe098444397
status: test
description: It is extremely abnormal for svchost.exe to spawn without any CLI arguments and is normally observed when a malicious process spawns the process and injects code into the process memory space.
references:
    - https://web.archive.org/web/20180718061628/https://securitybytes.io/blue-team-fundamentals-part-two-windows-processes-759fe15965e2
author: David Burkett, @signalblur
date: 2019-12-28
modified: 2022-06-27
tags:
    - attack.privilege-escalation
    - attack.stealth
    - attack.t1055
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        CommandLine|endswith: 'svchost.exe'
        Image|endswith: '\svchost.exe'
    filter:
        - ParentImage|endswith:
              - '\rpcnet.exe'
              - '\rpcnetp.exe'
        - CommandLine: null  # no CommandLine value available
    condition: selection and not filter
falsepositives:
    - Rpcnet.exe / rpcnetp.exe which is a lojack style software. https://www.blackhat.com/docs/us-14/materials/us-14-Kamlyuk-Kamluk-Computrace-Backdoor-Revisited.pdf
level: high

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    CommandLine|endswith: 'svchost.exe'
    Image|endswith: '\svchost.exe'

Stage 2: `not filter`

filter:
    - ParentImage|endswith:
          - '\rpcnet.exe'
          - '\rpcnetp.exe'
    - CommandLine: null

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`CommandLine`	is_null	(no value, null check)	`excludes:CommandLine`
`ParentImage`	ends_with	`\rpcnet.exe`	`excludes:ParentImage` `field:"ParentImage" value:"\rpcnet.exe"`
`ParentImage`	ends_with	`\rpcnetp.exe`	`excludes:ParentImage` `field:"ParentImage" value:"\rpcnetp.exe"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	ends_with	`svchost.exe`	`field:"CommandLine" kind:ends_with value:"svchost.exe"`
`Image`	ends_with	`\svchost.exe` corpus 23 (sigma 22, kusto 1)	`field:"Image" kind:ends_with value:"\svchost.exe"`