Suspicious Service DACL Modification Via Set-Service Cmdlet

Severity: high
Author: Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects suspicious DACL modifications via the "Set-Service" cmdlet using the "SecurityDescriptorSddl" flag (Only available with PowerShell 7) that can be used to hide services or make them unstopable

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1543.003` Create or Modify System Process: Windows Service
Privilege Escalation	`T1543.003` Create or Modify System Process: Windows Service

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\pwsh.exe'
OriginalFileName: pwsh.dll

Stage 2: `all of selection_sddl_flag`

or:
CommandLine|contains: '-SecurityDescriptorSddl '
CommandLine|contains: '-sd '

Stage 3: `all of selection_set_service`

or:
CommandLine|contains: ';;;BA'
CommandLine|contains: ';;;IU'
CommandLine|contains: ';;;SU'
CommandLine|contains: ';;;SY'
CommandLine|contains: ';;;WD'
CommandLine|contains: 'D;;'
CommandLine|contains: 'Set-Service '

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.

Field	Kind	Values
`CommandLine`	match	`-SecurityDescriptorSddl` corpus 2 (sigma 2) `-sd` corpus 2 (sigma 2) `;;;BA` `;;;IU` `;;;SU` `;;;SY` `;;;WD` `D;;` `Set-Service` corpus 2 (sigma 2)
`Image`	ends_with	`\pwsh.exe` corpus 140 (sigma 140)
`OriginalFileName`	eq	`pwsh.dll` corpus 72 (sigma 68, splunk 4)