Windows: Suspicious Child Process Created as System

Rule ID

PH_Rule_SIGMA_2543

Default Status

Enabled

Description

Detection of child processes spawned with SYSTEM privileges by parents with LOCAL SERVICE or NETWORK SERVICE accounts. This rule is adapted from https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_susp_child_process_as_system_.yml

Severity

MITRE ATT&CK® Tactics

Defense Evasion

Defense Evasion consists of techniques that adversaries use to avoid detection throughout their compromise. Techniques used for defense evasion include uninstalling/disabling security software or obfuscating/encrypting data and scripts. Adversaries also leverage and abuse trusted processes to hide and masquerade their malware. Other tactics’ techniques are cross-listed here when those techniques include the added benefit of subverting defenses.

https://attack.mitre.org/tactics/TA0005

MITRE ATT&CK® Techniques

T1134.002

Access Token Manipulation: Create Process with Token

Adversaries may create a new process with a duplicated token to escalate privileges and bypass access controls. An adversary can duplicate a desired access token with "DuplicateToken(Ex)" and use it with "CreateProcessWithTokenW" to create a new process running under the security context of the impersonated user. This is useful for creating a new process under the security context of a different user.

https://attack.mitre.org/techniques/T1134/002

Impacts

Server

Data Source

Windows Sysmon via FortiSIEM Agent

Detection

Correlation

Remediation Guidance

No remediation guidance specified

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.

Filter

SubPattern Definitions

SubPattern Name: Filter

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

eventType="Win-Sysmon-1-Create-Process" AND (userGrp REGEXP ".*AUTHORI.*|.*AUTORI.*" AND userGrp REGEXP ".*\\LOCAL SERVICE|.*\\NETWORK SERVICE" AND user REGEXP ".*AUTHORI.*|.*AUTORI.*" AND user REGEXP ".*\\SYSTEM|.*\\Syst.me|.*\\C.CTEMA" AND integrityLevel="System") AND ((procName NOT REGEXP ".*\\rundll32\.exe" OR command NOT REGEXP ".*DavSetCookie.*"))

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID

command,hostName,integrityLevel,procName,user,userGrp

Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

COUNT(*) >= 1

Incident Attribute Mapping

This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.

The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern

command = Filter.command,
hostName = Filter.hostName,
integrityLevel = Filter.integrityLevel,
procName = Filter.procName,
user = Filter.user,
userGrp = Filter.userGrp

FortiSIEM Rules