Detects Nimbus Manticore (UNC1549) agent implant featuring data exfiltration and remote control.

Hunt Hypothesis

This hunt hypothesis targets the deployment of the Nimbus Manticore (UNC1549) agent implant to identify adversaries establishing persistent footholds for covert data exfiltration and remote command execution. Proactive hunting in Azure Sentinel is essential because this critical-severity threat leverages advanced stealth mechanisms that may evade standard signature-based detections, requiring behavioral analysis to uncover early-stage compromise indicators.

YARA Rule

rule MAL_APT_Nimbus_Manticore_Agent_May26 {
   meta:
      description = "Detects Nimbus Manticore (UNC1549) agent implant featuring data exfiltration and remote control."
      author = "Jonathan Peters (Nextron Systems)"
      date = "2026-05-28"
      reference = "https://www.nextron-systems.com/2026/06/01/detecting-nimbus-manticore-and-their-sideloading-infection-chains/"
      hash = "dfa1e3137a032ee8561a1cd5e1a0f71a10bebb36aef7c336c878638a9c1239ee"
      score = 80
   strings:
      $a1 = "Chrome/146.0.0.0 Safari/537.36" wide
      $a2 = ".azurewebsites.net" wide

      $s1 = "/agent/poll?token=" wide fullword
      $s2 = "/agent/init" wide fullword
      $s3 = "/agent/result" wide fullword
   condition:
      uint16(0) == 0x5a4d
      and 1 of ($a*) 
      and 1 of ($s*)
      or 3 of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 5 string patterns in its detection logic.

References

• https://www.nextron-systems.com/2026/06/01/detecting-nimbus-manticore-and-their-sideloading-infection-chains/
• Source Rule

False Positive Guidance

Here are 3-5 specific false positive scenarios for the Nimbus Manticore (UNC1549) detection rule, including tailored filters and exclusions:

• Endpoint Protection Agent Self-Updates

  • Scenario: The organization’s primary EDR solution (e.g., CrowdStrike Falcon or Microsoft Defender for Endpoint) performs a scheduled nightly update of its telemetry agent. These agents often utilize similar implant mechanisms and network behaviors (data exfiltration to cloud endpoints, remote policy control) that mimic the Manticore signature.
  • Filter/Exclusion: Create an exclusion rule based on the specific process name and path of the EDR agent (e.g., C:\Program Files\CrowdStrike\fsqa.exe or C:\Windows\System32\DPSvc.exe) where the parent process is the Windows Update service (usoc.dll).

• Enterprise Backup & Archiving Jobs

  • Scenario: Scheduled backup jobs utilizing tools like Veeam Agent for Microsoft Windows or Commvault perform large-scale data exfiltration to a central repository. These jobs often establish persistent connections and execute remote control commands to manage snapshots, triggering the “data exfiltration” logic of the rule.
  • Filter/Exclusion: Exclude traffic originating from known backup service accounts (e.g., DOMAIN\BackupSvc) running specific executable paths (e.g., C:\Program Files\Veeam\Endpoint Backup\veeamagent.exe) during defined maintenance windows (e.g., 02:00–04:00 daily).

• IT Asset Management & Patch Deployment

  • Scenario: Automated patch management tools such as Ivanti Neurons or SCCM (Configuration Manager) deploy updates and inventory data. These agents frequently implant small payloads to gather hardware/software inventory (exfiltration) and push remote configuration changes, closely resembling