Windows Defender Context Menu Removed

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

Detects the use of reg.exe or PowerShell to delete the Windows Defender context menu handler registry keys. This action removes the "Scan with Microsoft Defender" option from the right-click menu for files, directories, and drives. Attackers may use this technique to hinder manual, on-demand scans and reduce the visibility of the security product.

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

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\powershell.exe'
Image|endswith: '\powershell_ise.exe'
Image|endswith: '\pwsh.exe'
Image|endswith: '\reg.exe'
OriginalFileName: PowerShell.EXE
OriginalFileName: powershell_ise.EXE
OriginalFileName: pwsh.dll
OriginalFileName: reg.exe

Stage 2: `all of selection_action`

or:
CommandLine|contains: Remove-Item
CommandLine|contains: del
CommandLine|contains: 'ri '

Stage 3: `all of selection_reg_path`

CommandLine|contains: '\shellex\ContextMenuHandlers\EPP'

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	`Remove-Item` `\shellex\ContextMenuHandlers\EPP` `del` `ri`
`Image`	ends_with	`\powershell.exe` corpus 143 (sigma 143) `\powershell_ise.exe` corpus 27 (sigma 27) `\pwsh.exe` corpus 140 (sigma 140) `\reg.exe` corpus 46 (sigma 46)
`OriginalFileName`	eq	`PowerShell.EXE` corpus 64 (sigma 60, splunk 4) `powershell_ise.EXE` corpus 8 (sigma 4, splunk 4) `pwsh.dll` corpus 72 (sigma 68, splunk 4) `reg.exe` corpus 29 (sigma 29)