Cerber4

Hunt Hypothesis

This hypothesis posits that adversaries are establishing persistent footholds by leveraging the specific behavioral patterns defined in the Cerber4 rule to evade standard alerting thresholds. Proactive hunting for this activity within Azure Sentinel is critical to validate these subtle indicators before they escalate into significant security incidents, ensuring early detection of low-severity but high-impact threats.

YARA Rule

rule cerber4{
meta:
        author = "pekeinfo"
        date = "2016-09-09"
        description = "Cerber4"
strings:
        $a = {8B 0D ?? ?? 43 00 51 8B 15 ?? ?? 43 00 52 E8 C9 04 00 00 83 C4 08 89 45 FC A1 ?? ?? 43 00 3B 05 ?? ?? 43 00 72 02}

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 5 specific false positive scenarios for the Cerber4 detection rule in an enterprise environment, including suggested filters and exclusions:

• Scheduled Antivirus Full Scans by Endpoint Managers

  • Scenario: Enterprise endpoint protection tools (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint, or Trend Micro) initiate scheduled full-system scans during off-hours. These jobs often trigger high-volume file enumeration and process creation events that mimic the behavior Cerber4 flags as suspicious lateral movement or data exfiltration.
  • Filter/Exclusion: Create an exclusion rule to ignore alerts where the Process Name matches known AV scanner executables (e.g., MsMpEng.exe, Cortex.sys) and the User Account is a local system account (e.g., NT AUTHORITY\SYSTEM). Additionally, filter by time windows corresponding to maintenance schedules (e.g., 02:00–06:00 UTC).

• Identity Management Synchronization Jobs

  • Scenario: Automated synchronization tasks using tools like Microsoft Azure AD Connect, Okta Workforce Identity, or SailPoint run periodically to update user attributes, group memberships, and password hashes. These jobs generate a burst of authentication logs and directory service modifications that can be misinterpreted as unauthorized bulk account changes or privilege escalation attempts by Cerber4.
  • Filter/Exclusion: Exclude events originating from the specific Service Accounts used for synchronization (e.g., svc-adconnect, okta-sync-agent). Filter based on the Source IP being a static management subnet and correlate with known job execution logs in the SIEM to suppress alerts during the 15-minute window of sync completion.

• Patch Management Deployment Windows

  • Scenario: During monthly patch cycles, tools such as **Microsoft SCCM (Configuration