ThreatFox: Stealc IOCs

Hunt Hypothesis

This detection rule identifies adversary activity consistent with the Stealc malware family by monitoring for nine specific Indicators of Compromise (IOCs) known to facilitate data exfiltration and persistence. Proactively hunting for these signatures in Azure Sentinel is critical because early identification of Stealc IOCs allows the SOC team to rapidly isolate affected assets before sensitive credentials or intellectual property are compromised.

IOC Summary

Malware Family: Stealc Total IOCs: 9 IOC Types: sha256_hash, sha1_hash, md5_hash, url, ip:port

KQL: Ip Hunt

// Hunt for network connections to known malicious IPs
// Source: ThreatFox - Stealc
let malicious_ips = dynamic(["91.202.233.134", "94.26.83.155"]);
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(["91.202.233.134", "94.26.83.155"]);
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://94.26.83.155/312b423bf6dd463f8d15.php"]);
UrlClickEvents
| where Url has_any (malicious_urls)
| project Timestamp, AccountUpn, Url, ActionType, IsClickedThrough
| order by Timestamp desc

KQL: Hash Hunt

// Hunt for files matching known malicious hashes
// Source: ThreatFox - Stealc
let malicious_hashes = dynamic(["716608d7e9a26e980f916e73792abcb86bbb21fb949436b7f359afcaf730b078", "1dd66d9ee5902947bda7eb381fa256877a646879", "dc903b2967c0c943084a0d5c0d131cf1", "d3f9acfa6119f28d666e25d7e078570a", "1095cf2951bbc8b1ecd33798afad192449a102aa1b976fb60bf566a08d693587", "53e0bf97e465842a9130aae1fcdf0968273f6d14"]);
DeviceFileEvents
| where SHA256 in (malicious_hashes) or SHA1 in (malicious_hashes) or MD5 in (malicious_hashes)
| project Timestamp, DeviceName, FileName, FolderPath, SHA256, InitiatingProcessFileName
| 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 suggested filters or exclusions:

• Endpoint Protection Scanning Operations

  • Scenario: The organization’s primary EDR solution (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint) performs a scheduled deep scan of the C:\ProgramData\Stealc directory. During this process, the scanner generates multiple network connections to internal update servers and DNS queries that match Stealc IOCs due to shared IP ranges or domain names used by both the threat and legitimate enterprise infrastructure.
  • Suggested Filter: Exclude traffic originating from known EDR service accounts (e.g., NT SERVICE\CrowdStrikeService, LocalSystem) where the process path matches the installed EDR binary location, specifically filtering out connections to internal IP subnets used for patch management.

• Software Deployment via SCCM/Intune

  • Scenario: The IT Operations team deploys a new version of a legitimate third-party utility (e.g., “StealGuard” or a similarly named internal tool) using Microsoft Endpoint Configuration Manager (SCCM). The deployment package triggers the creation of scheduled tasks and network beaconing to the vendor’s update servers, which coincidentally share IOCs with the Stealc malware family.
  • Suggested Filter: Create an exclusion for processes launched by ccmexec.exe or Microsoft.IntuneManagementExtension that connect to specific whitelisted FQDNs associated with the deployed software vendor, excluding alerts where the parent process is a known deployment engine.

• Legacy Application Maintenance Jobs

  • Scenario: A legacy financial reporting application runs a nightly batch job via Windows Task Scheduler (schtasks.exe). This job invokes a script that establishes connections to an external data provider using specific IP addresses and ports that