is str mandibule gen1

Hunt Hypothesis

This detection targets the execution of Mandible Gen1 malware artifacts, indicating an adversary attempting to establish persistence or conduct reconnaissance within the environment. The SOC team should proactively hunt for this signature in Azure Sentinel to identify early-stage infections that may evade standard high-severity alerts and prevent lateral movement before escalation occurs.

YARA Rule

rule is__str_mandibule_gen1 {
	meta:
		author = "unixfreaxjp"
		date = "2018-05-31"
	strings:
		$str01 = "shared arguments too big" fullword nocase wide ascii
		$str02 = "self inject pid: %" fullword nocase wide ascii
		$str03 = "injected shellcode at 0x%lx" fullword nocase wide ascii        	
		$str04 = "target pid: %d" fullword nocase wide ascii        	
		$str05 = "mapping '%s' into memory at 0x%lx" fullword nocase wide ascii
		$str06 = "shellcode injection addr: 0x%lx" fullword nocase wide ascii
		$str07 = "loading elf at: 0x%llx" fullword nocase wide ascii
	condition:
                4 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 7 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are specific false positive scenarios for the is_str_mandibule_gen1 detection rule, tailored for an enterprise environment:

• Antivirus Definition Updates via Microsoft Defender

  • Scenario: The daily automated update cycle of Microsoft Defender Antivirus triggers a scan where the engine writes new signature files and executable components to the %ProgramData%\Microsoft\Windows Defender\Definitions directory. These newly written binaries often match the is_str_mandibule_gen1 YARA pattern due to shared library structures or embedded strings common in security tooling.
  • Filter/Exclusion: Exclude file paths containing \Microsoft\Windows Defender\ and process names MsMpEng.exe from the alert scope, specifically targeting write operations during the scheduled maintenance window (e.g., 02:00–04:00 UTC).

• Enterprise Software Deployment via SCCM/MECM

  • Scenario: During a scheduled patch Tuesday deployment, Microsoft Endpoint Configuration Manager (SCCM) executes ccmexec.exe to distribute and install application updates. The installation package includes a generic runtime component that instantiates the is_str_mandibule_gen1 signature upon extraction to the %Temp% folder before finalization.
  • Filter/Exclusion: Create an exclusion for process paths starting with \Program Files (x86)\Microsoft Configuration Manager\ and filter events where the parent process is ccmexec.exe, limiting the alert to non-business hours or specific deployment job IDs.

• Database Maintenance Jobs via SQL Server Agent

  • Scenario: A nightly maintenance job in Microsoft SQL Server executes a backup and integrity check routine (DBCC CHECKDB). The sqlservr.exe process spawns temporary worker threads that generate log files and utility binaries containing the specific string patterns defined in the YARA rule, particularly when handling large transaction