ThreatFox: Mirai IOCs

Hunt Hypothesis

This hypothesis posits that adversaries are leveraging known Mirai botnet indicators of compromise to establish persistent command-and-control channels or initiate lateral movement within the network. The SOC team should proactively hunt for these specific IOCs in Azure Sentinel to rapidly identify and contain early-stage IoT device infections before they escalate into large-scale distributed denial-of-service attacks.

IOC Summary

Malware Family: Mirai Total IOCs: 2 IOC Types: sha256_hash, url

KQL: Url Hunt

// Hunt for access to known malicious URLs
// Source: ThreatFox - Mirai
let malicious_urls = dynamic(["http://94.154.43.5/mips"]);
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 - Mirai
let malicious_hashes = dynamic(["a5b42be0041bff5a4e521412014c2e7029ff08df7e9746fb4d923d40cee0e7d7"]);
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 — Mirai

False Positive Guidance

Here are specific false positive scenarios for the ThreatFox: Mirai IOCs rule in an enterprise environment, along with recommended filters and exclusions:

• Network Inventory & Asset Discovery Scans

  • Scenario: Automated network discovery tools (e.g., SolarWinds NPM, ** Lansweeper**, or Nmap) frequently scan the entire IP range to identify connected devices. These scanners often probe IoT endpoints (cameras, printers) on ports commonly targeted by Mirai (TCP 23/SSH, TCP 80/HTTP), generating legitimate traffic that matches Mirai’s initial connection signatures.
  • Filter/Exclusion: Create a whitelist exclusion for the source IP addresses of the scanning appliances and specific scan service accounts. Additionally, filter out traffic where the destination port is standard management ports (e.g., TCP 23) but the packet payload size indicates a discovery handshake rather than an active command execution.

• Scheduled Firmware Update Jobs

  • Scenario: Enterprise IoT management platforms (such as Cisco Meraki Dashboard, FortiGate SD-WAN, or Microsoft Endpoint Configuration Manager) execute scheduled jobs to push firmware updates to legacy devices like IP cameras and VoIP phones. These update agents often connect to external vendor repositories using the same IP ranges or domains identified in Mirai IOCs, triggering alerts during the download phase.
  • Filter/Exclusion: Exclude traffic originating from known internal patch management servers (e.g., WSUS servers) destined for specific IoT VLANs during defined maintenance windows (e.g., Sundays 02:00–04:00 UTC). Implement a rule to suppress alerts if the destination port is HTTPS (443) and the User-Agent header contains the vendor’s update client string.

• Cloud-Based Device Management Gateways

  • Scenario: In hybrid environments,