ThreatFox: Stealc IOCs

Hunt Hypothesis

This detection rule identifies adversary activity linked to the Stealc malware by monitoring specific Indicators of Compromise (IOCs) that signal potential data exfiltration or command-and-control communication. A SOC team should proactively hunt for these signatures in Azure Sentinel to rapidly isolate compromised endpoints and prevent lateral movement before the threat escalates into a broader incident.

IOC Summary

Malware Family: Stealc Total IOCs: 2 IOC Types: url, domain

KQL: Domain Hunt

// Hunt for DNS queries to known malicious domains
// Source: ThreatFox - Stealc
let malicious_domains = dynamic(["friendihelp.info"]);
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 - Stealc
let malicious_urls = dynamic(["https://friendihelp.info/fast.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 specific false positive scenarios and corresponding filters/exclusions for the ThreatFox: Stealc IOCs detection rule in an enterprise environment:

• Endpoint Protection Engine Updates: The organization’s EDR solution (e.g., CrowdStrike Falcon or Microsoft Defender for Endpoint) periodically downloads definition updates from a vendor repository that shares a common IP range or certificate hash with known Stealc infrastructure.

  • Suggested Filter: Exclude network traffic and process executions originating from the specific EDR service account (e.g., svc-crowdstrike or LocalSystem) where the parent process is the EDR agent binary (e.g., csagent.exe or MsMpEng.exe).

• Automated Backup Job Execution: A scheduled backup task (e.g., Veeam Agent or Commvault) running via Task Scheduler connects to a cloud storage gateway that utilizes an IP address flagged in the ThreatFox IOC list for Stealc.

  • Suggested Filter: Create an exclusion rule based on the specific Scheduled Task name (e.g., VeeamBackupJob) and the parent process (vbr.exe), ensuring it only applies during defined maintenance windows (e.g., 02:00–04:00 daily).

• Third-Party SaaS Integration Sync: An internal HR or CRM application (e.g., Workday or Salesforce) performs a nightly data synchronization with an external API endpoint that is currently listed in the Stealc IOC set due to shared hosting infrastructure.

  • Suggested Filter: Whitelist the specific outbound connection by filtering on the destination URL domain and the initiating application executable (e.g., workday-agent.exe), rather than blocking based solely on IP address.

• Software Deployment via Configuration Management: The IT team uses a tool like Microsoft SCCM or Ansible to push software updates, where the deployment server connects to a