ThreatFox: WannaCryptor IOCs

Hunt Hypothesis

This hunt hypothesis targets WannaCryptor ransomware activity by identifying indicators such as unpatched system exploitation via EternalBlue, phishing-driven initial access, and subsequent file encryption patterns that signal active lateral movement. Proactive hunting in Azure Sentinel is critical to detect early-stage registry modifications and process injection behaviors before widespread data encryption occurs, enabling rapid containment of this high-severity threat.

IOC Summary

Malware Family: WannaCryptor Total IOCs: 3 IOC Types: md5_hash, sha256_hash, sha1_hash

KQL: Hash Hunt

// Hunt for files matching known malicious hashes
// Source: ThreatFox - WannaCryptor
let malicious_hashes = dynamic(["9f762f6edf24c297545951a74df4d45d", "f2257d01dde12339f8bc370eabc74fa487e116b47f61f2094472885b9e4cb631", "106ae11053f255c0c4e4472ce084e57b56488bb1"]);
DeviceFileEvents
| where SHA256 in (malicious_hashes) or SHA1 in (malicious_hashes) or MD5 in (malicious_hashes)
| project Timestamp, DeviceName, FileName, FolderPath, SHA256, InitiatingProcessFileName
| order by Timestamp desc

Required Data Sources

References

• ThreatFox — WannaCryptor

False Positive Guidance

False Positive Scenarios: ThreatFox: WannaCryptor IOCs

• Scenario 1: Scheduled Antivirus Database Updates

  • Context: Enterprise endpoint protection suites (e.g., Microsoft Defender for Endpoint or Symantec Endpoint Protection) often perform scheduled signature and engine updates during off-hours. These processes frequently involve the creation of temporary files, registry key modifications under HKLM\Software, and network traffic to vendor update servers that mimic the file encryption and lateral movement behaviors associated with WannaCryptor.
  • Suggested Filter/Exclusion: Create a rule exclusion for specific process names (e.g., MsMpEng.exe, Symantec Antivirus Client) when they are running under the context of scheduled tasks like “Antimalware Scan” or “Update Service.” Additionally, exclude network traffic destined for known vendor update domains (e.g., *.microsoft.com, *.symantec.com) during defined maintenance windows.

• Scenario 2: Automated Backup and Archiving Jobs

  • Context: Enterprise backup solutions such as Veeam Backup & Replication or Commvault execute heavy file I/O operations to archive data, often changing file extensions (e.g., appending .vbk or .bck) and compressing large datasets. This mass file modification can trigger the “signs of file encryption” logic in the detection rule, as the backup engine writes new encrypted blocks that resemble ransomware activity.
  • Suggested Filter/Exclusion: Implement a filter to exclude processes belonging to known backup agents (e.g., Veeam.Backup.Service.exe, CommServe.exe) and their child processes. Furthermore, add an exclusion for file extension changes occurring within specific backup directories or when the process user context is a dedicated service account (e.g., DOMAIN\BackupSvc).

• **Scenario 3: Patch Management Deployment via WSUS/