ThreatFox: Stealc IOCs

Hunt Hypothesis

This detection identifies adversary activity consistent with the Stealc malware family by monitoring for specific indicators of compromise across the Azure Sentinel environment. Proactively hunting for these signatures is critical to rapidly contain potential data exfiltration and credential theft before they escalate into broader organizational breaches.

IOC Summary

Malware Family: Stealc Total IOCs: 3 IOC Types: url

KQL: Url Hunt

// Hunt for access to known malicious URLs
// Source: ThreatFox - Stealc
let malicious_urls = dynamic(["http://144.31.57.94/350be244a2f97a3a4ca8.php", "https://t.me/still_stellc", "http://89.110.104.237/46893b462dca7432.php"]);
UrlClickEvents
| where Url has_any (malicious_urls)
| project Timestamp, AccountUpn, Url, ActionType, IsClickedThrough
| order by Timestamp desc

Required Data Sources

References

• ThreatFox — Stealc

False Positive Guidance

Here are 5 specific false positive scenarios for the ThreatFox: Stealc IOCs detection rule in an enterprise environment, including suggested filters or exclusions:

• Endpoint Protection Scanning of Quarantine Archives

  • Scenario: The organization’s EDR solution (e.g., CrowdStrike Falcon or Microsoft Defender) performs a deep scan of the C:\ProgramData\ThreatFox\Quarantine directory. This action triggers a file access event for known Stealc IOCs that were previously ingested into the threat intelligence platform and stored locally as reference samples, mimicking an active infection.
  • Filter/Exclusion: Exclude process paths matching the EDR service executable (e.g., C:\Program Files\CrowdStrike\fs.exe or MsMpEng.exe) when accessing files within the ThreatFox quarantine directory.

• Scheduled Vulnerability Assessment Scans

  • Scenario: A nightly scheduled job running Tenable Nessus or Qualys scans endpoints for known vulnerabilities. The scanner downloads and executes a local agent update package that contains embedded Stealc IOCs (as part of the vulnerability definition database), causing the detection logic to flag the scan activity as a potential threat execution.
  • Filter/Exclusion: Create an exclusion rule based on the Scheduled Task name (e.g., \Microsoft\Tenable\Nessus Agent Update) or filter by the parent process being the Windows Task Scheduler service (svchost.exe -k netsvcs).

• Software Deployment via Configuration Management

  • Scenario: The IT Operations team uses Ansible or SCCM (System Center Configuration Manager) to deploy a new security patch. During the deployment, the package extracts a temporary installer that includes a library file matching a Stealc IOC hash. This occurs during standard business hours on domain-joined workstations