Cerber5

Hunt Hypothesis

This detection rule identifies anomalous authentication patterns associated with the Cerber5 adversary behavior, which may indicate early-stage reconnaissance or lateral movement attempts within the Azure environment. Proactively hunting for this signal is critical to validate potential false negatives in existing alerting logic and ensure that low-severity indicators are not overlooked before they escalate into significant security incidents.

YARA Rule

rule cerber5{
meta:
  author = "pekeinfo"
  date = "2016-12-02"
  description = "Cerber5"
strings:
  $a = {83 C4 04 A3 ?? ?? ?? 00 C7 45 ?? ?? ?? ?? 00 8B ?? ?? C6 0? 56 8B ?? ?? 5? 68 ?? ?? 4? 00 FF 15 ?? ?? 4? 00 50 FF 15 ?? ?? 4? 00 A3 ?? ?? 4? 00 68 1D 10 00 00 E8 ?? ?? FF FF 83 C4 04 ?? ?? ??}
  
condition:
  1 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 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the Cerber5 detection rule in an enterprise environment, including recommended filters and exclusions:

• Automated Patch Deployment via SCCM/Intune

  • Scenario: During nightly maintenance windows, System Center Configuration Manager (SCCM) or Microsoft Intune agents push critical security patches to thousands of endpoints. This triggers a high volume of file integrity changes and process executions that mimic the behavioral patterns Cerber5 is designed to catch as suspicious activity.
  • Filter/Exclusion: Create an exclusion for processes running under the CCMExec.exe (SCCM) or Microsoft.IntuneManagementExtension.exe context. Additionally, filter events occurring between 01:00 and 04:00 UTC where the source IP belongs to the internal patch management subnet (e.g., 10.20.30.0/24).

• Scheduled Antivirus Full Scans

  • Scenario: Enterprise-grade antivirus solutions like CrowdStrike Falcon or SentinelOne perform scheduled full-system scans every morning at 08:00 AM. These scans generate massive amounts of I/O operations and temporary file creation/deletion, which can be misinterpreted by Cerber5 as unauthorized data exfiltration or anomalous process spawning.
  • Filter/Exclusion: Exclude events where the parent process is identified as FalconService.exe (CrowdStrike) or SentinelOneAgent.exe. Implement a rule to suppress alerts for file access patterns matching the specific scan signature hash list maintained by the AV vendor’s update feed.

• Database Backup Jobs via SQL Server Agent

  • Scenario: The nightly backup routine managed by Microsoft SQL Server Agent triggers large data transfers and log truncation operations on database servers. These activities involve high-privilege service accounts (e.g., `DOMAIN\svc