codeCrypter031Tibbar

Hunt Hypothesis

This detection identifies potential Tibbar-based malware activity that utilizes code encryption to evade static analysis and obscure malicious payloads within the environment. Proactive hunting for this behavior is essential in Azure Sentinel to uncover stealthy threats that may bypass signature-based defenses by analyzing encrypted code structures before they establish persistence or initiate lateral movement.

YARA Rule

rule codeCrypter031Tibbar
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 50 58 53 5B 90 BB [3] 00 FF E3 90 CC CC CC 55 8B EC 5D C3 CC CC CC CC CC CC CC CC CC CC CC }

condition:
		$a0 at pe.entry_point
}

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 codeCrypter031Tibbar detection rule, along with recommended filters and exclusions:

• Scenario: Microsoft Office Macro Execution in Excel

  • Context: Users frequently open Excel workbooks containing embedded VBA macros that utilize code obfuscation techniques similar to the Tibbar signature. When a user opens a report from Finance or HR, the macro engine initializes and triggers the rule.
  • Suggested Filter/Exclusion: Create an exclusion for processes running under EXCEL.EXE where the parent process is also EXCEL.EXE (indicating a child window) or specifically exclude file paths containing \Microsoft Office\root\Office16\. Additionally, filter out events where the file extension is .xlsm or .xlam located in trusted network shares.

• Scenario: Antivirus Heuristic Scanning by CrowdStrike Falcon

  • Context: The endpoint protection suite (e.g., CrowdStrike Falcon) performs real-time heuristic scanning on executable files. Its internal scanner often employs code packing and encryption mechanisms that mimic the behavior of the codeCrypter031Tibbar signature, causing a self-trigger when scanning its own components or third-party installers.
  • Suggested Filter/Exclusion: Exclude processes where the image path contains \CrowdStrike\ or \Falcon\. Implement a logic filter to suppress alerts if the Parent Image Name is falcon-sensor.exe and the event type indicates “File Scan” rather than “Process Execution.”

• Scenario: Scheduled Deployment via SCCM/Intune

  • Context: During off-hours, System Center Configuration Manager (SCCM) or Microsoft Intune pushes software updates. The deployment agents often utilize encrypted installers (e.g., MSI packages wrapped in a crypt