ThreatFox: WannaCryptor IOCs

Hunt Hypothesis

This detection rule identifies adversary behavior associated with the WannaCryptor ransomware family by monitoring for specific indicators of compromise such as file encryption patterns and cryptocurrency transaction signals within Azure Sentinel. Proactively hunting for these IOCs is critical to enable early intervention before widespread data encryption occurs, thereby minimizing operational downtime and preventing potential financial loss from ransom demands.

IOC Summary

Malware Family: WannaCryptor Total IOCs: 12 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(["c3f59fc053ff6ade13667c98d808b9ba", "7fb8b06a9ac3c0c6b475948d1b981586cea76a2fc53f57c54163352fd90f0c63", "b86596258e715a1e6847a2e67f4346fe15eb1712", "4eedba281d6273d442925536aa61b3df", "5961d2b84eced872ba81a0a270b0f7a49dddab7b", "656a5cf0c4ea3a166c813b24dc4bce8403afb4305504805d654764712caf5a96", "f2930bf9aa785c2f10884dd59e814e33eef096fb", "301b4c0650787760609a2f4535ab9ff3", "9be73437f744884e7ee2af167deb9ffb93551419c2ad9b4f8852d3f7c5f3bb8b", "91269eb3c084956392ddaf6a60139fd5", "6e96fe30490bed142959566daf8be3f66bd3645c", "9d769ee6c8365659c7a703f221caab25f1a972bf1324dc3623d08e2eaa5b4856"]);
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

Here are 4 specific false positive scenarios for the ThreatFox: WannaCryptor IOCs rule, tailored for an enterprise environment with suggested filters and exclusions:

• Scenario: Scheduled Antivirus Full Scans on Shared Drives

  • Context: Enterprise Endpoint Protection platforms (e.g., Microsoft Defender for Endpoint or Symantec Endpoint Protection) often perform scheduled full scans of network shares during off-hours. These scanners may generate file access patterns, specific registry modifications, or process behaviors that mimic the encryption and file-locking activities of WannaCryptor.
  • Suggested Filter/Exclusion: Create an exclusion rule for processes running under the SYSTEM account on known backup servers (e.g., Hostname: DC-BACKUP-01) during the maintenance window (e.g., 02:00–04:00). Specifically, exclude process hashes associated with MsMpEng.exe or Symantec Antivirus Console when they interact with .docx, .xlsx, and .pdf extensions on mapped drives.

• Scenario: Automated Document Conversion via Office 365 Pro Plus

  • Context: In environments utilizing Microsoft Office 365, the background service OfficeClickToRun.exe frequently performs batch conversions of legacy documents (e.g., converting .doc to .docx) or updates templates. This activity involves rapid file creation and modification that can trigger IOCs related to mass file encryption or extension changes typical of ransomware.
  • Suggested Filter/Exclusion: Implement a logic filter to suppress alerts where the parent process is OfficeClickToRun.exe (or winword.exe) and the user context is a known service account (e.g., CN=Office-Service-Account). Additionally, exclude file extensions that are part of the standard Office suite conversion chain (.doc,