detect xxmm in memory

Hunt Hypothesis

This rule detects adversaries executing shellcode or payloads directly within process memory to evade traditional file-based detection mechanisms. Proactive hunting for this behavior in Azure Sentinel is critical because it identifies stealthy execution techniques that often precede lateral movement and data exfiltration before they trigger higher-severity alerts.

YARA Rule

rule xxmm {
          meta:
            description = "detect xxmm in memory"
            author = "JPCERT/CC Incident Response Group"
            rule_usage = "memory scan"
            reference = "internal research"

          strings:
            $v1 = "setupParameter:"
            $v2 = "loaderParameter:"
            $v3 = "parameter:"

          condition: all 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 3 string patterns in its detection logic.

References

• internal research
• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the “detect xxmm in memory” rule within an enterprise environment, including suggested filters and exclusions:

• Enterprise Endpoint Protection Scans

  • Scenario: The organization’s EDR agent (e.g., CrowdStrike Falcon or Microsoft Defender for Endpoint) performs a scheduled deep memory scan. During this process, the scanner loads its proprietary xxmm signature module directly into the system RAM to analyze running processes against known threat indicators. This legitimate activity mimics the presence of an unknown xxmm artifact in memory.
  • Filter/Exclusion: Create an exclusion rule for the specific EDR service executable (e.g., C:\Program Files\CrowdStrike\fs.exe) and exclude any memory signatures loaded by processes running under the SYSTEM or NT AUTHORITY\NETWORK SERVICE accounts during standard business hours (08:00–18:00).

• Automated Patch Management Deployments

  • Scenario: During a weekly maintenance window, the patch management tool (e.g., Ivanti Neurons or SCCM) deploys updates to critical servers. The deployment agent injects a temporary xxmm configuration module into memory to verify driver compatibility before applying the update. This injection is transient and expected but triggers the detection logic as an “unknown” memory object.
  • Filter/Exclusion: Exclude alerts originating from the patch management service account (e.g., DOMAIN\PatchAdmin) specifically when the parent process matches known deployment tools like ccmexec.exe or IvAgentService.exe. Additionally, filter out events occurring between 02:00 and 04:00 UTC on Tuesdays.

• Database Backup and Recovery Operations

  • Scenario: A scheduled SQL Server backup job utilizes a third-party utility (e.g., V