Potentially Suspicious Windows App Activity

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

Detects potentially suspicious child process of applications launched from inside the WindowsApps directory. This could be a sign of a rogue ".appx" package installation/execution

Event coverage

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

Stages and Predicates

Stage 1: `selection_parent`

ParentImage|contains: 'C:\Program Files\WindowsApps\'

Stage 2: `1 of selection_susp_img`

or:
Image|endswith: '\cmd.exe'
Image|endswith: '\cscript.exe'
Image|endswith: '\mshta.exe'
Image|endswith: '\powershell.exe'
Image|endswith: '\powershell_ise.exe'
Image|endswith: '\pwsh.exe'
Image|endswith: '\regsvr32.exe'
Image|endswith: '\rundll32.exe'
Image|endswith: '\wscript.exe'

Stage 3: `1 of selection_susp_cli`

or:
CommandLine|contains: Base64
CommandLine|contains: Invoke-
CommandLine|contains: 'cmd /c'

Stage 4: `not 1 of filter_optional_*`

or:
or:
Image|endswith: '\cmd.exe'
Image|endswith: '\powershell.exe'
Image|endswith: '\pwsh.exe'
ParentImage|endswith: '\WindowsTerminal.exe'
ParentImage|contains: ':\Program Files\WindowsApps\Microsoft.WindowsTerminal'
Image|endswith: '\cmd.exe'
ParentImage|startswith: 'C:\Program Files\WindowsApps\Microsoft.SysinternalsSuite'

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	`Base64` `Invoke-` corpus 5 (sigma 5) `cmd /c` corpus 4 (sigma 4)
`Image`	ends_with	`\cmd.exe` corpus 92 (sigma 92) `\cscript.exe` corpus 64 (sigma 64) `\mshta.exe` corpus 57 (sigma 57) `\powershell.exe` corpus 143 (sigma 143) `\powershell_ise.exe` corpus 27 (sigma 27) `\pwsh.exe` corpus 140 (sigma 140) `\regsvr32.exe` corpus 57 (sigma 57) `\rundll32.exe` corpus 76 (sigma 76) `\wscript.exe` corpus 64 (sigma 64)
`ParentImage`	ends_with	`\WindowsTerminal.exe` corpus 3 (sigma 3)
`ParentImage`	match	`:\Program Files\WindowsApps\Microsoft.WindowsTerminal` `C:\Program Files\WindowsApps\`
`ParentImage`	starts_with	`C:\Program Files\WindowsApps\Microsoft.SysinternalsSuite`

Potentially Suspicious Windows App Activity

Event coverage

Stages and Predicates

Stage 1: selection_parent

Stage 2: 1 of selection_susp_img

Stage 3: 1 of selection_susp_cli

Stage 4: not 1 of filter_optional_*

Indicators

Stage 1: `selection_parent`

Stage 2: `1 of selection_susp_img`

Stage 3: `1 of selection_susp_cli`

Stage 4: `not 1 of filter_optional_*`