Windows AppX Deployment Full Trust Package Installation

Status: experimental
Severity: medium
Log source: product windows, service appxdeployment-server
Author: Michael Haag, Swachchhanda Shrawan Poudel (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects the installation of MSIX/AppX packages with full trust privileges which run with elevated privileges outside normal AppX container restrictions

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1204.002` User Execution: Malicious File
Defense Impairment	`T1553.005` Subvert Trust Controls: Mark-of-the-Web Bypass

Event coverage

Provider	Event	Title
AppXDeployment-Server	Event ID 400	Deployment DeploymentOperation operation with target volume MountPoint on Package PackageFullName from: Path finished successfully.

Rule body yaml

title: Windows AppX Deployment Full Trust Package Installation
id: e54279c7-4910-4e2c-902c-c56a25b549f6
status: experimental
description: Detects the installation of MSIX/AppX packages with full trust privileges which run with elevated privileges outside normal AppX container restrictions
references:
    - https://www.splunk.com/en_us/blog/security/msix-weaponization-threat-detection-splunk.html
author: Michael Haag, Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-11-03
tags:
    - attack.execution
    - attack.defense-impairment
    - attack.t1204.002
    - attack.t1553.005
logsource:
    product: windows
    service: appxdeployment-server
detection:
    selection:
        EventID: 400
        HasFullTrust: true
    filter_main_legitpath:
        PackageSourceUri|startswith:
            - 'file:///C:/Program%20Files/'
            - 'file:///C:/Program%20Files%20(x86)/'
    filter_main_microsoft:
        - PackageSourceUri|startswith: 'https://go.microsoft.com/fwlink/?linkid'
        - PackageSourceUri|contains:
              - '.cdn.microsoft.com'
              - '.cdn.office.net/'
    filter_main_callerprocess:
        CallingProcess|startswith:
            - 'sysprep.exe'
            - 'svchost.exe,AppReadiness'
    filter_optional_x_update:
        PackageSourceUri|startswith: 'x-windowsupdate://'
    filter_optional_microsoftclient:
        PackageFullName|startswith: 'MicrosoftWindows.Client.'
    condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
    - Some legitimate applications installation which have been missed from filtering can generate fps, thus baselining and tuning is recommended before deploying to production
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_* and not 1 of filter_optional_*

Stage 1: `selection`

selection:
    EventID: 400
    HasFullTrust: true

Stage 2: `not filter_main_*`

filter_main_legitpath:
    PackageSourceUri|startswith:
        - 'file:///C:/Program%20Files/'
        - 'file:///C:/Program%20Files%20(x86)/'
filter_main_microsoft:
    - PackageSourceUri|startswith: 'https://go.microsoft.com/fwlink/?linkid'
    - PackageSourceUri|contains:
          - '.cdn.microsoft.com'
          - '.cdn.office.net/'
filter_main_callerprocess:
    CallingProcess|startswith:
        - 'sysprep.exe'
        - 'svchost.exe,AppReadiness'

Stage 3: `not filter_optional_*`

filter_optional_x_update:
    PackageSourceUri|startswith: 'x-windowsupdate://'
filter_optional_microsoftclient:
    PackageFullName|startswith: 'MicrosoftWindows.Client.'

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`CallingProcess`	starts_with	`svchost.exe,AppReadiness`
`CallingProcess`	starts_with	`sysprep.exe`
`PackageSourceUri`	match	`.cdn.microsoft.com`
`PackageSourceUri`	match	`.cdn.office.net/`
`PackageSourceUri`	starts_with	`file:///C:/Program%20Files%20(x86)/`
`PackageSourceUri`	starts_with	`file:///C:/Program%20Files/`
`PackageSourceUri`	starts_with	`https://go.microsoft.com/fwlink/?linkid`
`PackageFullName`	starts_with	`MicrosoftWindows.Client.`
`PackageSourceUri`	starts_with	`x-windowsupdate://`

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
`HasFullTrust`	eq	`true` corpus 2 (sigma 1, splunk 1)

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Windows AppX Deployment Full Trust Package Installation

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`

Stage 3: `not filter_optional_*`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Windows AppX Deployment Full Trust Package Installation

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter_main_*

Stage 3: not filter_optional_*

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`

Stage 3: `not filter_optional_*`