ThreatFox: Tsundere IOCs

Hunt Hypothesis

This hunt detects adversary behavior linked to the Tsundere threat actor by searching for specific indicators of compromise that signal active reconnaissance or initial access attempts within the network. Proactively hunting for these IOCs in Azure Sentinel is critical because early identification of Tsundere’s unique signatures allows the SOC team to rapidly isolate affected assets and prevent lateral movement before the adversary establishes a persistent foothold.

IOC Summary

Malware Family: Tsundere Total IOCs: 2 IOC Types: ip:port

KQL: Ip Hunt

// Hunt for network connections to known malicious IPs
// Source: ThreatFox - Tsundere
let malicious_ips = dynamic(["91.92.33.250", "93.152.224.44"]);
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(["91.92.33.250", "93.152.224.44"]);
DeviceNetworkEvents
| where RemoteIP in (malicious_ips)
| project Timestamp, DeviceName, RemoteIP, RemotePort, InitiatingProcessFileName, ActionType
| order by Timestamp desc

Required Data Sources

References

• ThreatFox — Tsundere

False Positive Guidance

Here are 5 specific false positive scenarios for the ThreatFox: Tsundere IOCs detection rule, tailored for an enterprise environment, along with suggested filters or exclusions:

• Endpoint Protection Policy Updates via CrowdStrike Falcon

  • Scenario: The Enterprise Security Operations Center (SOC) pushes a new definition update containing IoC signatures to the endpoint fleet. When the CrowdStrike Falcon sensor on a Domain Controller downloads and validates these definitions, it generates network traffic or file hash events that match Tsundere’s known benign infrastructure IPs or certificate hashes used by the vendor.
  • Suggested Filter: Exclude source IP ranges associated with the CrowdStrike update servers (e.g., 137.254.x.x) and specific process names (C:\Program Files\CrowdStrike\csfalcon.exe) from triggering this rule during scheduled maintenance windows (e.g., 02:00–04:00 UTC).

• Scheduled Microsoft Defender for Endpoint Threat Intelligence Sync

  • Scenario: A nightly scheduled task (Microsoft-Windows-Security-Auditing or Defender Antivirus Service) runs to synchronize the local threat intelligence database with Microsoft’s cloud. This process initiates outbound connections to Microsoft’s content delivery network, which may utilize IP addresses or domain names that overlap with Tsundere’s benign infrastructure IOCs (specifically regarding certificate validation).
  • Suggested Filter: Create an exclusion for traffic originating from the Microsoft Defender Antivirus service (MsMpEng.exe) destined for Microsoft Azure Content Delivery Network IP blocks, specifically filtering out events where the Event ID corresponds to a successful policy sync rather than a new threat detection.

• Internal Vulnerability Scanning with Tenable Nessus

  • Scenario: The vulnerability management team executes a weekly scan using Tenable Nessus agents installed on critical servers.