Modify Group Policy Settings

Severity: medium
Author: frack113
Source: upstream

Detect malicious GPO modifications can be used to implement many other malicious behaviors.

MITRE ATT&CK coverage

Tactic	Techniques
Privilege Escalation	`T1484.001` Domain or Tenant Policy Modification: Group Policy Modification
Defense Evasion	`T1484.001` Domain or Tenant Policy Modification: Group Policy Modification

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_reg`

or:
Image|endswith: '\reg.exe'
OriginalFileName: reg.exe

Stage 2: `all of selection_path`

CommandLine|contains: '\SOFTWARE\Policies\Microsoft\Windows\System'

Stage 3: `all of selection_key`

or:
CommandLine|contains: EnableSmartScreen
CommandLine|contains: GroupPolicyRefreshTime
CommandLine|contains: GroupPolicyRefreshTimeDC
CommandLine|contains: GroupPolicyRefreshTimeOffset
CommandLine|contains: GroupPolicyRefreshTimeOffsetDC
CommandLine|contains: ShellSmartScreenLevel

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	`EnableSmartScreen` `GroupPolicyRefreshTime` `GroupPolicyRefreshTimeDC` `GroupPolicyRefreshTimeOffset` `GroupPolicyRefreshTimeOffsetDC` `ShellSmartScreenLevel` `\SOFTWARE\Policies\Microsoft\Windows\System`
`Image`	ends_with	`\reg.exe` corpus 46 (sigma 46)
`OriginalFileName`	eq	`reg.exe` corpus 29 (sigma 29)