ThreatFox: Unknown Stealer IOCs

Hunt Hypothesis

This detection rule identifies potential data exfiltration activities by matching network and endpoint telemetry against three critical Indicators of Compromise (IOCs) linked to the Unknown Stealer malware family. Proactive hunting for these specific IOCs within Azure Sentinel is essential to rapidly identify early-stage infections before adversaries can establish persistence or escalate their impact on sensitive organizational assets.

IOC Summary

Malware Family: Unknown Stealer Total IOCs: 3 IOC Types: ip:port, url

KQL: Ip Hunt

// Hunt for network connections to known malicious IPs
// Source: ThreatFox - Unknown Stealer
let malicious_ips = dynamic(["45.39.33.177"]);
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(["45.39.33.177"]);
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 - Unknown Stealer
let malicious_urls = dynamic(["https://mylovemarry.com", "http://45.39.33.177/peter.php"]);
UrlClickEvents
| where Url has_any (malicious_urls)
| project Timestamp, AccountUpn, Url, ActionType, IsClickedThrough
| order by Timestamp desc

Required Data Sources

References

• ThreatFox — Unknown Stealer

False Positive Guidance

Here are 4 specific false positive scenarios for the ThreatFox: Unknown Stealer IOCs rule, including targeted filters and exclusions suitable for an enterprise environment:

• Legitimate Endpoint Protection Scans

  • Scenario: The organization’s primary endpoint protection suite (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint, or Carbon Black) performs a scheduled “Full System Scan” during off-hours. These agents often generate network connections to update signature databases and upload telemetry, which may match the specific IOCs (hashes or URLs) defined in the Unknown Stealer hunt package.
  • Filter/Exclusion: Create an exclusion rule that filters out alerts where the Process Name matches known security agents (e.g., C:\Program Files\CrowdStrike\fsq.exe, MsMpEng.exe) and the User Account is a system service account (e.g., NT AUTHORITY\SYSTEM).

• Automated Software Deployment via Configuration Management

  • Scenario: A scheduled Microsoft SCCM (Configuration Manager) or Ansible job pushes a new application update to workstations. The deployment agent downloads the installer package from an internal repository server, triggering network traffic that aligns with the “Unknown Stealer” IOCs due to similar file hashes or destination IP ranges used by both the stealer and the deployment tool.
  • Filter/Exclusion: Exclude alerts where the Parent Process is a known configuration management agent (e.g., ccmsetup.exe, ansible-runner) and the Destination Port corresponds to internal repository ports (e.g., 80, 443) within the corporate IP range.

• Third-Party Cloud Backup Agents

  • Scenario: Enterprise backup solutions like Veeam, Rubrik, or **Acronis Cyber