ThreatFox: Unknown malware IOCs

Hunt Hypothesis

This detection rule identifies potential unknown malware infections by correlating ten distinct Indicators of Compromise (IOCs) that may evade signature-based defenses. The SOC team should proactively hunt for these IOCs in Azure Sentinel to rapidly isolate and investigate novel threats before they establish persistence or propagate laterally across the environment.

IOC Summary

Malware Family: Unknown malware Total IOCs: 10 IOC Types: url, domain

KQL: Domain Hunt

// Hunt for DNS queries to known malicious domains
// Source: ThreatFox - Unknown malware
let malicious_domains = dynamic(["popelkar.pro", "auth-clo-id.cc", "kinikar.pro"]);
DnsEvents
| where Name has_any (malicious_domains)
| project TimeGenerated, Computer, Name, IPAddresses, QueryType
| order by TimeGenerated desc

KQL: Url Hunt

// Hunt for access to known malicious URLs
// Source: ThreatFox - Unknown malware
let malicious_urls = dynamic(["https://chessco.co.za/", "https://bbinvinoveritas.com/", "https://alinais.ch/", "https://aacjuvenile.com/", "https://mail.assembleiadedeus.org.br/", "https://popelkar.pro/", "https://kinikar.pro/"]);
UrlClickEvents
| where Url has_any (malicious_urls)
| project Timestamp, AccountUpn, Url, ActionType, IsClickedThrough
| order by Timestamp desc

Required Data Sources

References

• ThreatFox — Unknown malware

False Positive Guidance

Here are 5 specific false positive scenarios for the ThreatFox: Unknown malware IOCs detection rule, along with targeted filters and exclusions:

• Scenario: Scheduled Antivirus Definition Updates

  • Context: Enterprise endpoints running Microsoft Defender for Endpoint or Symantec Endpoint Protection automatically download new definition signatures every morning. These updates often introduce new hash values (IOCs) that have not yet been ingested into the ThreatFox intelligence feed, triggering “Unknown” alerts.
  • Filter/Exclusion: Create a time-based exclusion window for the rule between 02:00 and 04:00 UTC on weekdays. Alternatively, filter out IOCs where the source process name matches MsMpEng.exe (Defender) or Symantec Antivirus.exe.

• Scenario: Internal Software Deployment via SCCM/Intune

  • Context: The IT team uses Microsoft Endpoint Configuration Manager (SCCM) or Microsoft Intune to push a new version of an internal custom application (e.g., “HR-Portal-v2.4.exe”) to 5,000 workstations. Since this is a proprietary binary not yet in the ThreatFox database, its hash triggers the rule upon installation on every machine.
  • Filter/Exclusion: Add a whitelist exclusion for the specific SHA-256 hash of the internal application installer. Additionally, filter out alerts where the Installation Source attribute indicates “System Center Configuration Manager” or “Intune Management Extension.”

• Scenario: Automated Patching Jobs via WSUS

  • Context: A nightly scheduled job runs on the Windows Server Update Services (WSUS) server to deploy critical security patches. The patch installation process generates temporary files and new executable versions that are not yet recognized by ThreatFox, causing a spike in unknown