PowerShell Defender Threat Severity Default Action Set to 'Allow' or 'NoAction'

Severity: high
Author: Matt Anderson (Huntress)
Source: upstream

Detects the use of PowerShell to execute the 'Set-MpPreference' cmdlet to configure Windows Defender's threat severity default action to 'Allow' (value '6') or 'NoAction' (value '9'). This is a highly suspicious configuration change that effectively disables Defender's ability to automatically mitigate threats of a certain severity level. An attacker might use this technique via the command line to bypass defenses before executing payloads.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1562.001` Impair Defenses: Disable or Modify Tools

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation
Security-Auditing	4688	A new process has been created.

Stages and Predicates

Stage 1: `all of selection_cmdlet`

CommandLine|contains: Set-MpPreference

Stage 2: `all of selection_action`

or:
CommandLine|contains: -HighThreatDefaultAction
CommandLine|contains: -LowThreatDefaultAction
CommandLine|contains: -ModerateThreatDefaultAction
CommandLine|contains: -SevereThreatDefaultAction
CommandLine|contains: '-htdefac '
CommandLine|contains: '-ltdefac '
CommandLine|contains: '-mtdefac '
CommandLine|contains: '-stdefac '

Stage 3: `all of selection_value`

or:
CommandLine|contains: 6
CommandLine|contains: 9
CommandLine|contains: Allow
CommandLine|contains: NoAction

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	`-HighThreatDefaultAction` `-LowThreatDefaultAction` `-ModerateThreatDefaultAction` `-SevereThreatDefaultAction` `-htdefac` `-ltdefac` `-mtdefac` `-stdefac` `6` `9` `Allow` corpus 2 (sigma 2) `NoAction` `Set-MpPreference`