Unsigned AppX Installation Attempt Using Add-AppxPackage - PsScript

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

Detects usage of the "Add-AppxPackage" or it's alias "Add-AppPackage" to install unsigned AppX packages

Event coverage

Provider	Event ID	Title
PowerShell	4104	Creating Scriptblock text (MessageNumber of MessageTotal).

Stages and Predicates

Stage 1: `all of selection_cmdlet`

or:
ScriptBlockText|contains: 'Add-AppPackage '
ScriptBlockText|contains: 'Add-AppxPackage '

Stage 2: `all of selection_flag`

ScriptBlockText|contains: ' -AllowUnsigned'

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
`ScriptBlockText`	match	`-AllowUnsigned` `Add-AppPackage` `Add-AppxPackage`

Neighbors

Broader alternatives (more inclusive than this rule)

These rules match a superset of what this rule catches. They cover the same events plus more. Use them if you want wider coverage and can absorb more false positives.

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Potential PowerShell Obfuscation via Special Character Overuse [elastic] (cross-vendor) (drops 1 filter this rule applies) (first-stage match only; downstream stages may differ)