r4 wiper 2

Hunt Hypothesis

The hypothesis is that the detected behavior may indicate the presence of a wiper malware variant using specific file modification patterns, which could be used to erase data and disrupt operations. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate potential data destruction threats early, especially in environments with sensitive or critical data.

YARA Rule

rule r4_wiper_2
{
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:
	// BIOS Extended Write
	$PhysicalDriveSTR = "\\\\.\\PhysicalDrive" wide
	$ExtendedWrite = { B4 43 B0 00 CD 13 }
condition:
	uint16(0) == 0x5a4d and uint16(uint32(0x3c)) == 0x4550 and all 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 cleanup or disk defragmentation using Windows Disk Defragmenter or CCleaner
  Filter/Exclusion: Check for presence of defrag.exe or ccleaner.exe in the process tree, or filter by process name.

• Scenario: Automated backup job using Veeam Backup & Replication or Commvault
  Filter/Exclusion: Filter by process names like veeam.exe or cvbackup.exe, or check for presence of known backup directories.

• Scenario: System update or patching task using Windows Update or WSUS
  Filter/Exclusion: Check for process names like wuauserv.exe or svchost.exe with associated update-related services.

• Scenario: Malware analysis or sandboxing environment using Cuckoo Sandbox or Joe Sandbox
  Filter/Exclusion: Filter by presence of sandbox-specific artifacts or known sandbox IP ranges, or check for presence of analysis tools like cuckoo.exe.

• Scenario: Administrative task such as disk cleanup or registry maintenance using Disk Cleanup or CCleaner
  Filter/Exclusion: Filter by process names like cleanmgr.exe or ccleaner.exe, or check for user context (e.g., non-administrator user).