ThreatFox: Stealc IOCs

Hunt Hypothesis

This hunt identifies potential compromise by matching network traffic or endpoint activity against known indicators of compromise associated with the Stealc malware family. Proactively hunting for these IOCs in Azure Sentinel allows the SOC to detect stealthy intrusions and lateral movement attempts before they escalate into a full-blown breach.

IOC Summary

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

KQL: Url Hunt

// Hunt for access to known malicious URLs
// Source: ThreatFox - Stealc
let malicious_urls = dynamic(["https://cloud-flare-authenticator.click", "https://update-microsoft-data.services"]);
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

• Scenario: A DevOps engineer uses a custom PowerShell script to audit and clean up stale temporary files in the C:\Users\Public\Temp directory, specifically targeting files with the .tmp extension that match a specific hash or size range defined in the Stealc IOC list.
  • Filter/Exclusion: Exclude alerts where the initiating process is powershell.exe or pwsh.exe and the parent process is a known CI/CD agent (e.g., jenkins.exe, gitlab-runner.exe) or a scheduled task named *TempCleanup*.
• Scenario: An IT support technician performs a manual disk cleanup on a user’s workstation using the built-in Windows “Disk Cleanup” utility (cleanmgr.exe) or a third-party tool like CCleaner, which may delete or move files matching the specific IOCs (e.g., specific registry keys or file paths) associated with Stealc.
  • Filter/Exclusion: Exclude alerts where the process name is cleanmgr.exe, ccleaner64.exe, or ccleaner32.exe, or where the command line contains arguments like /sageset or /run and the user belongs to the IT_Support or Desktop_Support security group.
• Scenario: A security team runs a YARA or Sigma rule scan across the environment to validate new detection coverage, intentionally creating test files or registry entries that match the Stealc IOCs to verify the detection engine is firing correctly.
  • Filter/Exclusion: Exclude alerts where the source IP address belongs to the Security_Team subnet (e.g., 10.20.30.0/24) or where the user account name contains sec_ or test_ (e.g., sec_analyst_01, `test_stealc