ThreatFox: Stealc IOCs

Hunt Hypothesis

This detection identifies adversary activity involving known Indicators of Compromise (IOCs) linked to the Stealc malware, which is frequently used in supply chain attacks and data exfiltration campaigns. A proactive hunt for these IOCs within Azure Sentinel is critical to rapidly identify early-stage infections and prevent lateral movement before sensitive data is compromised.

IOC Summary

Malware Family: Stealc Total IOCs: 2 IOC Types: url, ip:port

KQL: Ip Hunt

// Hunt for network connections to known malicious IPs
// Source: ThreatFox - Stealc
let malicious_ips = dynamic(["89.34.90.45"]);
CommonSecurityLog
| where DestinationIP in (malicious_ips) or SourceIP in (malicious_ips)
| project TimeGenerated, SourceIP, DestinationIP, DestinationPort, DeviceAction, Activity
| order by TimeGenerated desc

KQL: Ip Hunt Device

// Hunt in Defender for Endpoint network events
let malicious_ips = dynamic(["89.34.90.45"]);
DeviceNetworkEvents
| where RemoteIP in (malicious_ips)
| project Timestamp, DeviceName, RemoteIP, RemotePort, InitiatingProcessFileName, ActionType
| order by Timestamp desc

KQL: Url Hunt

// Hunt for access to known malicious URLs
// Source: ThreatFox - Stealc
let malicious_urls = dynamic(["https://proxy.checkverifybot.com"]);
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, along with targeted filters and exclusions:

• Scenario: Legitimate Endpoint Protection Scans

  • Context: Enterprise EDR agents (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint) frequently download signature updates or threat intelligence feeds from the internet. These downloads often match known Stealc IOCs because the vendor’s update servers share IP ranges or file hashes with the Stealc campaign data in ThreatFox.
  • Filter/Exclusion: Create a rule exclusion based on process names and parent processes. Exclude events where the ProcessName matches FalconSensor.exe, MsMpEng.exe, or DefenderService.exe AND the ParentImage is the same EDR service executable.

• Scenario: Scheduled Backup Jobs

  • Context: Automated backup solutions like Veeam, Commvault, or Acronis run nightly jobs that generate large log files and network traffic to cloud repositories. If these tools utilize a specific hashing algorithm or connect to a storage endpoint listed in the Stealc IOC set, they trigger alerts during their execution window (e.g., 02:00–04:00).
  • Filter/Exclusion: Implement a time-based exclusion combined with process path filtering. Exclude events occurring between 01:00 and 05:00 where the CommandLine contains keywords like “backup”, “sync”, or specific paths such as C:\Program Files\Veeam\Backup and Replication.

• Scenario: Software Deployment via SCCM/Intune

  • Context: System Center Configuration Manager (SCCM) or Microsoft Intune pushes application updates to thousands of endpoints simultaneously. The deployment agents often download packages from distribution points that may share