ThreatFox: WannaCryptor IOCs

Hunt Hypothesis

This hunt hypothesis targets adversary behavior where WannaCryptor ransomware infiltrates Azure environments through phishing vectors and unpatched system vulnerabilities to encrypt critical data and demand cryptocurrency payments. Proactively hunting for these specific IOCs in Azure Sentinel is essential to identify early-stage infection indicators before widespread file encryption causes significant operational disruption and data loss.

IOC Summary

Malware Family: WannaCryptor Total IOCs: 12 IOC Types: sha1_hash, sha256_hash, md5_hash

KQL: Hash Hunt

// Hunt for files matching known malicious hashes
// Source: ThreatFox - WannaCryptor
let malicious_hashes = dynamic(["ee2a0f806eea5db5f8ed4e22f52d1b2492e62a6b", "752b88ff4f0f5ea39ac1912c924f2f4d", "1963f2cceff182e761507020f6cd92e54cb5194d", "b0a87d0fcdd49c072364c4378dfc9f8b", "431e527d800caf5391917f79b07bb0650501ded29678edca8627007f629c1bad", "1da954be17c19b2e61d605097f1c7b29", "3b6603d9bd648152700076a8e00a0e23218fd642ce63b5b47891f9db9ec0172b", "48fca9f4433f79d8595fb75fe0940af8177b91b51068c132655472551b91af5a", "e7aae02abc7dc06ef69efeb1e98654dd69efd500", "993e330b2c80db36a50514c5fd50466c", "4caa645feeb04cad5af75a3c5024076e99560678584c84ae07950c9c106d2af0", "55e3f9a3ae32da95511ccff3c3b2fcdde3b87c7a"]);
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 detection rule in an enterprise environment, along with suggested filters or exclusions:

• Scheduled Antivirus Definition Updates via WSUS/SCCM

  • Scenario: Enterprise endpoint protection agents (e.g., Microsoft Defender, CrowdStrike) frequently download large definition updates or scan archives containing known WannaCryptor hash signatures from the internal Software Update Services (WSUS) or System Center Configuration Manager (SCCM). These legitimate downloads often match the IOCs associated with the ransomware’s distribution mechanism.
  • Filter/Exclusion: Exclude traffic originating from internal IP ranges of WSUS servers, SCCM management points, and known antivirus update repositories. Additionally, filter for processes running under high-privilege service accounts (e.g., NT AUTHORITY\SYSTEM) rather than standard user sessions during maintenance windows.

• Automated Backup and File Replication Jobs

  • Scenario: Scheduled backup solutions like Veeam, Commvault, or Microsoft Azure Backup often perform heavy file I/O operations that mimic ransomware encryption behavior. These jobs may access thousands of files simultaneously, generating network flows and process execution logs that trigger the “file encryption” logic of the detection rule, especially if the backup software utilizes similar cryptographic libraries as the threat signature.
  • Filter/Exclusion: Create an exclusion list for known backup service executables (e.g., VeeamAgent.exe, cvpserver.exe) and their associated scheduled tasks. Filter alerts where the source process is running under dedicated backup service accounts (e.g., BackupServiceAccount) and verify that the file modification volume aligns with historical baseline patterns for these specific jobs.

• Patch Management Deployment of Security Updates

  • Scenario: During monthly patch cycles, tools like Ivanti or Microsoft Endpoint Configuration Manager deploy security patches