ThreatFox: Stealc IOCs

Hunt Hypothesis

This hypothesis posits that adversaries are actively deploying Stealc infostealer malware within the Azure environment to exfiltrate sensitive credentials and browser data using known Indicators of Compromise (IOCs). The SOC team should proactively hunt for these specific IOCs in Sentinel because early detection of this high-severity threat is critical to preventing lateral movement and mitigating the risk of widespread credential theft before automated defenses trigger.

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(["176.65.144.73"]);
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(["176.65.144.73"]);
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(["http://176.65.144.73/312b423bf6dd463f8d15.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 for the ThreatFox: Stealc IOCs detection rule, along with suggested filters and exclusions tailored for an enterprise environment:

• Endpoint Security Scanning of Quarantine Folders

  • Scenario: When EDR agents (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint) perform scheduled deep scans or on-demand updates, they often extract known malware samples into temporary quarantine directories. If the Stealc IOCs include specific file hashes or network artifacts that match these benign test samples, the rule may trigger during routine scanning cycles.
  • Filter/Exclusion: Exclude processes running under the security vendor’s service account (e.g., svc-crowdstrike, Microsoft Defender Antivirus) and restrict the detection scope to exclude paths containing \Quarantine\, \Temp\, or \Samples\.

• Software Deployment via Configuration Management Tools

  • Scenario: During routine patch management or application deployment using tools like SCCM (System Center Configuration Manager), Ansible, or Intune, the deployment engine may download and stage installer packages that contain shared libraries or dependencies matching Stealc IOCs. This is common when deploying third-party utilities (e.g., PDF readers, browser updates) that utilize similar cryptographic signatures to known Stealc artifacts.
  • Filter/Exclusion: Create an exclusion for processes initiated by deployment service accounts (e.g., NT AUTHORITY\SYSTEM running ccmexec.exe, Ansible-Runner) and filter out network traffic originating from the internal software distribution point IP ranges during standard maintenance windows (e.g., 02:00 – 04:00 UTC).

• IT Administration and Manual Artifact Analysis

  • Scenario: Security analysts or system administrators often download threat intelligence feeds, malware samples, or forensic tools to their local workstations for manual analysis.