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Description

The following analytic identifies a modification to the Transcodedwallpaper file in the wallpaper theme directory to change the wallpaper of the host machine. This technique was seen in adversaries attempting to deface or change the desktop wallpaper of the targeted host. During our testing, the common process that affects or changes the wallpaper if a user changes it via desktop personalized setting is explorer.exe.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2022-08-25
  • Author: Teoderick Contreras, Splunk
  • ID: e11c3d90-5bc7-42ad-94cd-ba75db10d897

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1491 Defacement Impact
Kill Chain Phase
  • Actions On Objectives
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


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| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where Processes.process_path !="*\\Windows\\Explorer.EXE" by _time span=1h Processes.process_id Processes.process_name Processes.process Processes.dest Processes.process_guid  Processes.original_file_name 
| `drop_dm_object_name(Processes)` 
|rename process_guid as proc_guid 
| join proc_guid, _time [ 
| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Filesystem where Filesystem.file_path = "*\\AppData\\Roaming\\Microsoft\\Windows\\Themes\\TranscodedWallpaper" by _time span=1h Filesystem.dest Filesystem.file_create_time Filesystem.file_name Filesystem.file_path Filesystem.process_guid 
| `drop_dm_object_name(Filesystem)` 
|rename process_guid as proc_guid 
| fields file_name file_path process_name process_path process dest file_create_time _time proc_guid] 
| `windows_defacement_modify_transcodedwallpaper_file_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_defacement_modify_transcodedwallpaper_file_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • dest
  • file_create_time
  • file_name
  • file_path
  • process_name
  • process_path
  • process

How To Implement

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Filesystem node. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.

Known False Positives

3rd part software application can change the wallpaper. Filter is needed.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
9.0 30 30 modification or creation of transcodedwallpaper file by $process_name$ in $dest$

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

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