Detect Internal Defacement in Splunk
Adversaries may deface systems internal to an organization in an attempt to intimidate or mislead users, discrediting the integrity of those systems. This manifests most commonly as ransomware operators setting desktop wallpaper to display ransom notes (Black Basta, BlackCat, Qilin, INC Ransomware, Diavol, RansomHub), dropping ransom note text or HTML files across the filesystem, modifying Windows logon legal notice messages, renaming disk volume labels to attacker contact information (ShrinkLocker), or changing lock screen images. Destructive APT groups such as Lazarus Group and Gamaredon have also used desktop wallpaper replacement to display threatening messages after rendering systems inoperable. Internal defacement occurs late in the attack lifecycle — after primary objectives such as data exfiltration or file encryption have been completed — because it reveals adversary presence and marks the point of no return for the victim.
MITRE ATT&CK
- Tactic
- Impact
- Technique
- T1491 Defacement
- Sub-technique
- T1491.001 Internal Defacement
- Canonical reference
- https://attack.mitre.org/techniques/T1491/001/
SPL Detection Query
index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational"
(
(EventCode=13
(TargetObject="*\\Control Panel\\Desktop\\Wallpaper"
OR TargetObject="*\\PersonalizationCSP\\DesktopImagePath"
OR TargetObject="*\\PersonalizationCSP\\LockScreenImagePath"
OR TargetObject="*\\PersonalizationCSP\\DesktopImageStatus"
OR TargetObject="*\\Winlogon\\LegalNoticeText"
OR TargetObject="*\\Winlogon\\LegalNoticeCaption"))
OR
(EventCode=11
(TargetFilename="*README*" OR TargetFilename="*DECRYPT*" OR TargetFilename="*HOW_TO*"
OR TargetFilename="*RESTORE_FILES*" OR TargetFilename="*YOUR_FILES*"
OR TargetFilename="*RANSOM*" OR TargetFilename="*RECOVER_FILES*"
OR TargetFilename="*FILES_ENCRYPTED*" OR TargetFilename="*HELP_DECRYPT*"
OR TargetFilename="*HOW-TO-DECRYPT*" OR TargetFilename="*IMPORTANT_READ*")
(TargetFilename="*.txt" OR TargetFilename="*.html" OR TargetFilename="*.hta"
OR TargetFilename="*.bmp" OR TargetFilename="*.jpg" OR TargetFilename="*.png"))
OR
(EventCode=1
(Image="*\\cmd.exe")
CommandLine="*label *:*")
OR
(EventCode=1
(Image="*\\powershell.exe" OR Image="*\\pwsh.exe")
(CommandLine="*SystemParametersInfo*" OR CommandLine="*SPI_SETDESKWALLPAPER*"
OR CommandLine="*SetWallpaper*" OR CommandLine="*DesktopWallpaper*"))
)
| eval DefacementType=case(
EventCode=13 AND match(TargetObject, "(?i)(Wallpaper|DesktopImagePath|DesktopImageStatus)"), "WallpaperChange",
EventCode=13 AND match(TargetObject, "(?i)(LockScreen)"), "LockScreenChange",
EventCode=13 AND match(TargetObject, "(?i)(LegalNotice)"), "LogonMessageChange",
EventCode=11, "RansomNoteDropped",
EventCode=1 AND match(CommandLine, "(?i)label\s+[a-zA-Z]:"), "DiskLabelModified",
EventCode=1 AND (match(Image, "(?i)(powershell|pwsh)") OR match(CommandLine, "(?i)(SystemParametersInfo|SetWallpaper|DesktopWallpaper)")), "PSWallpaperSet",
true(), "Defacement"
)
| eval IndicatorValue=coalesce(TargetObject, TargetFilename, CommandLine, "-")
| eval InitiatingProcess=coalesce(Image, "-")
| eval NotLegitProc=if(match(Image, "(?i)(explorer|SystemSettings|SystemSettingsBroker|dllhost|winlogon)"), 0, 1)
| where DefacementType != "Defacement"
| where EventCode != 13 OR NotLegitProc=1
| table _time, host, User, DefacementType, IndicatorValue, InitiatingProcess, CommandLine
| sort - _timeMulti-vector internal defacement detection using Sysmon event logs covering three primary signals: (1) Registry value set events (EventCode 13) monitoring wallpaper, lock screen, and Windows logon message registry keys — the mechanism used by Black Basta, BlackCat, Qilin, INC Ransomware, and Diavol to display ransom notes; (2) File creation events (EventCode 11) matching ransom note naming patterns (README, DECRYPT, HOW_TO, RESTORE_FILES) with common text and image extensions used by ransomware to leave payment instructions in every directory; (3) Process creation events (EventCode 1) for disk volume label commands (ShrinkLocker email-labeling technique) and PowerShell-based wallpaper changes via SystemParametersInfo API. Registry changes are filtered to exclude standard Windows wallpaper-setting processes to reduce false positives from legitimate personalization.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Group Policy applying corporate wallpaper or logon banners via gpsvc.exe — registry changes appear from SYSTEM context and match affected policy registry paths; correlate with Event ID 5136 in Security log for authorized GPO changes
- IT administrators setting LegalNoticeText/Caption for compliance baselines using reg.exe or PowerShell from a known administrative workstation — review against change management records
- Software installers creating README or documentation files during package installation — typically originate from msiexec.exe, setup.exe, or a known installer image path targeting program directory subdirectories
- Disk provisioning or storage automation scripts labeling volumes during system build — should be traceable to an approved provisioning account and imaging workflow timeframe
Other platforms for T1491.001
Testing Methodology
Validate this detection against 5 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Set Desktop Wallpaper via Registry to Simulate Ransom Note Display
Expected signal: Sysmon EventCode 13: TargetObject=HKCU\Control Panel\Desktop\Wallpaper, Details=%TEMP%\ransom_wallpaper.txt, Image=reg.exe. Sysmon EventCode 1: Process Create for reg.exe with CommandLine containing 'Control Panel\Desktop' and '/v Wallpaper'. MDE DeviceRegistryEvents: ActionType=RegistryValueSet, RegistryKey contains 'Control Panel\Desktop', RegistryValueName=Wallpaper, InitiatingProcessFileName=reg.exe.
- Test 2Set Desktop Wallpaper via PowerShell SystemParametersInfo API
Expected signal: Sysmon EventCode 1: Process Create for powershell.exe with CommandLine containing 'SystemParametersInfo'. Sysmon EventCode 13: TargetObject=HKCU\Control Panel\Desktop\Wallpaper with Details pointing to the test file (SystemParametersInfo updates this registry key). MDE DeviceProcessEvents: ProcessCommandLine contains 'SystemParametersInfo', FileName=powershell.exe.
- Test 3Modify Windows Logon Legal Notice to Simulate Ransom Demand at Login
Expected signal: Sysmon EventCode 13 (two events): TargetObject=HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\LegalNoticeCaption and \LegalNoticeText, Image=reg.exe, User=[current user]. Requires elevation (HKLM write). MDE DeviceRegistryEvents: ActionType=RegistryValueSet, RegistryKey contains 'Winlogon', RegistryValueName in (LegalNoticeCaption, LegalNoticeText), InitiatingProcessFileName=reg.exe.
- Test 4Drop Ransom Note Files Across Multiple Directories
Expected signal: Sysmon EventCode 11 (six events): TargetFilename for each README_DECRYPT.txt file created across the six directories, Image=cmd.exe. MDE DeviceFileEvents: ActionType=FileCreated, FileName=README_DECRYPT.txt, InitiatingProcessFileName=cmd.exe, FolderPath showing six different directories. The hunting query (UniqueDirectories > 5) will trigger on this test.
- Test 5Rename Disk Volume Label via CMD (ShrinkLocker Technique)
Expected signal: Sysmon EventCode 1: Process Create for cmd.exe or label.exe (label is a built-in cmd command that may appear as cmd.exe /c label). CommandLine contains 'label C:' and 'ArgusDefacementTest'. MDE DeviceProcessEvents: FileName=cmd.exe, ProcessCommandLine matches regex for 'label [drive]:'. Security Event ID 4688 if process creation auditing is enabled.
References (13)
- https://attack.mitre.org/techniques/T1491/001/
- https://www.varonis.com/blog/vmware-esxi-in-the-line-of-ransomware-fire
- https://web.archive.org/web/20160303200515/https:/operationblockbuster.com/wp-content/uploads/2016/02/Operation-Blockbuster-Destructive-Malware-Report.pdf
- https://www.minerva-labs.com/blog/new-black-basta-ransomware-hijacks-windows-fax-service/
- https://blogs.blackberry.com/en/2022/05/black-basta-rebrand-of-conti-or-something-new
- https://www.microsoft.com/en-us/security/blog/2022/06/13/the-many-lives-of-blackcat-ransomware/
- https://securelist.com/shrinklocker-ransomware-tools-and-targets/113108/
- https://www.splunk.com/en_us/blog/security/shrinklocker-ransomware-detection-on-the-radar.html
- https://www.cybereason.com/blog/threat-analysis-inc-ransomware
- https://www.secureworks.com/research/gold-ionic
- https://research.checkpoint.com/2021/indra-hackers-behind-recent-attacks-on-iran/
- https://cert.ee/en/2021/01/gamaredon-group-malware-distributed-in-ukraine/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1491.001/T1491.001.md
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