Replace Desktop Wallpaper by Powershell

Status: test
Severity: low
Log source: product windows, category ps_script
Author: frack113
Source: github.com/SigmaHQ/sigma

An adversary may deface systems internal to an organization in an attempt to intimidate or mislead users. This may take the form of modifications to internal websites, or directly to user systems with the replacement of the desktop wallpaper

MITRE ATT&CK coverage

Tactic	Techniques
Impact	`T1491.001` Defacement: Internal Defacement

Event coverage

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

Rule body yaml

title: Replace Desktop Wallpaper by Powershell
id: c5ac6a1e-9407-45f5-a0ce-ca9a0806a287
status: test
description: |
    An adversary may deface systems internal to an organization in an attempt to intimidate or mislead users.
    This may take the form of modifications to internal websites, or directly to user systems with the replacement of the desktop wallpaper
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1491.001/T1491.001.md
author: frack113
date: 2021-12-26
tags:
    - attack.impact
    - attack.t1491.001
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection_1:
        ScriptBlockText|contains|all:
            - 'Get-ItemProperty'
            - 'Registry::'
            - 'HKEY_CURRENT_USER\Control Panel\Desktop\'
            - 'WallPaper'
    selection_2:
        ScriptBlockText|contains: SystemParametersInfo(20,0,*,3)
    condition: 1 of selection_*
falsepositives:
    - Unknown
level: low

Stages and Predicates

Stage 0: `condition`

1 of selection_*

Stage 1: `selection_1`

selection_1:
    ScriptBlockText|contains|all:
        - 'Get-ItemProperty'
        - 'Registry::'
        - 'HKEY_CURRENT_USER\Control Panel\Desktop\'
        - 'WallPaper'

Stage 2: `selection_2`

selection_2:
    ScriptBlockText|contains: SystemParametersInfo(20,0,*,3)

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	`Get-ItemProperty` corpus 2 (sigma 2) `HKEY_CURRENT_USER\Control Panel\Desktop\` `Registry::` `SystemParametersInfo(20,0,*,3)` `WallPaper`

`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)

Replace Desktop Wallpaper by Powershell

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_1`

Stage 2: `selection_2`

Indicators

Keyboard shortcuts

Search operators

Replace Desktop Wallpaper by Powershell

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_1

Stage 2: selection_2

Indicators

Stage 0: `condition`

Stage 1: `selection_1`

Stage 2: `selection_2`