Cerber5b

Hunt Hypothesis

This detection rule identifies potential reconnaissance or lateral movement activities associated with the Cerber5b signature within the Azure Sentinel environment. Proactively hunting for this behavior allows the SOC team to uncover early-stage adversary footprints that may otherwise remain undetected due to the rule’s low severity classification, ensuring a more comprehensive threat posture before escalation occurs.

YARA Rule

rule cerber5b{
meta:
  author = "pekeinfo"
  date = "2016-12-20"
  description = "Cerber5b"
strings:
  $a={8B ?? ?8 ?? 4? 00 83 E? 02 89 ?? ?8 ?? 4? 00 68 ?C ?9 4? 00 [0-6] ?? ?? ?? ?? ?? ?8 ?? 4? 00 5? FF 15 ?? ?9 4? 00 89 45 ?4 83 7D ?4 00 75 02 EB 12 8B ?? ?0 83 C? 06 89 ?? ?0 B? DD 03 00 00 85}  
condition:
  $a
}

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 Cerber5b detection rule in an enterprise environment, including suggested filters or exclusions:

• Scenario: Automated Patch Deployment via SCCM/Intune

  • Context: The System Center Configuration Manager (SCCM) or Microsoft Intune agent performs scheduled software updates during maintenance windows. This triggers the Cerber5b rule due to rapid file creation/modification and process spawning across multiple endpoints simultaneously, mimicking a lateral movement attack.
  • Suggested Filter/Exclusion: Create an exclusion for processes running under the CcmExec.exe (SCCM) or Microsoft.IntuneManagementExtension.exe service accounts. Additionally, filter events occurring only between 02:00 and 04:00 UTC on weekdays to align with maintenance windows.

• Scenario: Enterprise Antivirus Real-Time Scanning

  • Context: The endpoint protection suite (e.g., CrowdStrike Falcon or SentinelOne) initiates a deep scan of the C:\Users\Public directory. This activity generates high-volume file access and hash calculation events that Cerber5b flags as suspicious data exfiltration or unauthorized script execution.
  • Suggested Filter/Exclusion: Exclude parent process names containing CrowdStrike Falcon Sensor, SentinelOne Agent, or specific AV vendor executables (e.g., MsMpEng.exe). Apply a logic filter to ignore events where the destination path matches known antivirus quarantine directories (e.g., \ProgramData\Microsoft\Windows Defender\Scans\Quarantine).

• Scenario: Scheduled SQL Database Backup Jobs

  • Context: A nightly SQL Server Agent job executes a full database backup, writing large .bak files to a Network Attached Storage (NAS) share. The Cerber5b rule detects the high I/O throughput and network connection