ThreatFox: Stealc IOCs

Hunt Hypothesis

This hypothesis posits that adversaries are actively deploying the Stealc infostealer to exfiltrate sensitive credentials and financial data from Azure workloads using known Indicators of Compromise (IOCs). Proactively hunting for these specific IOCs in Azure Sentinel is critical because early detection of Stealc’s initial infection vectors can prevent lateral movement and mitigate significant data loss before the malware establishes persistence.

IOC Summary

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

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, including suggested filters and exclusions tailored for an enterprise environment:

• Endpoint Protection Scanning of Quarantine Archives

  • Scenario: Enterprise Endpoint Detection and Response (EDR) solutions like CrowdStrike Falcon or SentinelOne frequently download threat intelligence updates or quarantine suspicious files. During these routine scans, the EDR engine may extract a compressed archive containing known Stealc IOCs (e.g., specific hash values of stealc.dll or update.exe) for analysis, triggering the detection even though no actual infection occurred on the host.
  • Filter/Exclusion: Exclude processes originating from the primary EDR service account (e.g., SYSTEM, NT AUTHORITY\CRSVC, or specific user IDs like svc-sentinelone). Additionally, filter out file paths located strictly within vendor quarantine directories (e.g., C:\ProgramData\CrowdStrike\Quarantine or C:\SentinelOne\Quarantine).

• Automated Patch Management and Software Deployment

  • Scenario: Scheduled deployment jobs using tools like Microsoft Endpoint Configuration Manager (MECM/SCCM) or Ivanti Neurons often distribute software updates that include third-party libraries. If a legitimate application update contains a component with a hash matching the Stealc IOC list, the installation process will generate the alert during the execution of the installer (msiexec.exe or setup.exe) running under the deployment service account.
  • Filter/Exclusion: Create an exclusion for processes launched by known patch management services (e.g., ccmexec.exe, IvantiAgent.exe). Filter specifically for events occurring during defined maintenance windows where the source IP belongs to the internal Patch Management Server subnet.

• **IT Security