ThreatFox: Brute Ratel C4 IOCs

Hunt Hypothesis

This hunt hypothesis targets adversaries leveraging Brute Ratel C4 infrastructure to establish persistent command and control channels or deliver initial payloads within the Azure environment. Proactive hunting for these specific IOCs is critical because early detection of this known threat actor allows the SOC team to disrupt lateral movement and data exfiltration before the adversary fully establishes a foothold in the cloud tenant.

IOC Summary

Malware Family: Brute Ratel C4 Total IOCs: 2 IOC Types: ip:port

KQL: Ip Hunt

// Hunt for network connections to known malicious IPs
// Source: ThreatFox - Brute Ratel C4
let malicious_ips = dynamic(["54.65.16.199", "54.248.1.253"]);
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(["54.65.16.199", "54.248.1.253"]);
DeviceNetworkEvents
| where RemoteIP in (malicious_ips)
| project Timestamp, DeviceName, RemoteIP, RemotePort, InitiatingProcessFileName, ActionType
| order by Timestamp desc

Required Data Sources

References

• ThreatFox — Brute Ratel C4

False Positive Guidance

Here are specific false positive scenarios for the ThreatFox: Brute Ratel C4 IOCs detection rule in an enterprise environment, along with recommended filters or exclusions:

• Scheduled Endpoint Protection Scans

  • Scenario: Enterprise-wide scheduled scans using tools like CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint often initiate network connections to their respective update servers and cloud management consoles. If the Brute Ratel C4 IOCs include specific IP ranges or domains used by these vendors (or if the malware mimics legitimate vendor traffic), a mass scan event across 50+ workstations could trigger thousands of alerts simultaneously.
  • Filter/Exclusion: Create an exclusion rule that suppresses alerts originating from known Endpoint Protection Service Accounts (e.g., svc_falcon_agent, defender_svc) or restrict the alert to only fire when the destination port is not a standard management port (e.g., exclude traffic on ports 80, 443, and vendor-specific high-numbered ports like 8021/9965).

• Patch Management Deployment Jobs

  • Scenario: During weekly maintenance windows, automated patching tools such as Ivanti, ManageEngine Patch Manager, or WSUS (Windows Server Update Services) push updates to the fleet. These tools frequently download large payloads from upstream repositories that may share IP addresses or domain names with the Brute Ratel C4 indicators. A legitimate bulk update job on a file server could be misidentified as malicious beaconing activity.
  • Filter/Exclusion: Implement a time-based filter to exclude alerts generated during defined maintenance windows (e.g., Sundays 02:00–06:00 UTC) for hosts belonging to the “Patch Management Target” security group. Additionally, whitelist specific **WSUS server