r4 wiper 1

Hunt Hypothesis

The hypothesis is that the detected behavior may indicate the presence of a wiper malware variant attempting to erase data by overwriting disk sectors. A SOC team should proactively hunt for this behavior in Azure Sentinel to identify and mitigate potential data destruction threats early, especially when combined with other indicators of compromise.

YARA Rule

rule r4_wiper_1
{
meta:
	source = "NCCIC Partner"
	date = "2017-12-12"
	report = "https://www.us-cert.gov/sites/default/files/publications/MAR-10135536.11.WHITE.pdf"
	report = "https://www.us-cert.gov/HIDDEN-COBRA-North-Korean-Malicious-Cyber-Activity"
strings:
	$mbr_code = { 33 C0 8E D0 BC 00 7C FB 50 07 50 1F FC BE 5D 7C 33 C9 41 81 F9 00 ?? 74 24 B4 43 B0 00 CD 13 FE C2 80 FA 84 7C F3 B2 80 BF 65 7C 81 05 00 04 83 55 02 00 83 55 04 00 83 55 06 00 EB D5 BE 4D 7C B4 43 B0 00 CD 13 33 C9 BE 5D 7C EB C5 }
	$controlServiceFoundlnBoth = { 83 EC 1C 57 68 3F 00 0F 00 6A 00 6A 00 FF 15 ?? ?? ?? ?? 8B F8 85 FF 74 44 8B 44 24 24 53 56 6A 24 50 57 FF 15 ?? ?? ?? ?? 8B 1D ?? ?? ?? ?? 8B F0 85 F6 74 1C 8D 4C 24 0C 51 6A 01 56 FF 15 ?? ?? ?? ?? 68 E8 03 00 00 FF 15 ?? ?? ?? ?? 56 FF D3 57 FF D3 5E 5B 33 C0 5F 83 C4 1C C3 33 C0 5F 83 C4 1C C3 }
condition:
	uint16(0) == 0x5a4d and uint16(uint32(0x3c)) == 0x4550 and any of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Scheduled system maintenance or cleanup task using Windows Task Scheduler
  Filter/Exclusion: Check for Task Scheduler job names or paths containing Cleanup, Maintenance, or Disk Cleanup in the event log or process tree.

• Scenario: Legitimate use of Windows Disk Imaging Tools (e.g., Macrium Reflect, Acronis True Image) for backup purposes
  Filter/Exclusion: Filter by process names like MacriumReflect.exe, AcronisTrueImage.exe, or check for known backup directories in the file system.

• Scenario: Windows Update or Group Policy deployment that temporarily modifies system files
  Filter/Exclusion: Exclude processes related to wuauclt.exe, gupdate.exe, or check for registry keys associated with Windows Update or Group Policy.

• Scenario: Disk Defragmentation task initiated by Defraggler or built-in Disk Defragmenter
  Filter/Exclusion: Filter by process names like Defraggler.exe or check for file system operations related to defrag or fragmentation.

• Scenario: Antivirus or Endpoint Protection tool performing a full system scan (e.g., Kaspersky, Bitdefender, Malwarebytes)
  Filter/Exclusion: Exclude processes like KavService.exe, bdagent.exe, or mbam.exe, and filter by known safe file access patterns during scans.