detect Agenttesla in memory

Hunt Hypothesis

This hypothesis posits that adversaries are deploying the AgentTesla information stealer within Azure-hosted workloads to exfiltrate sensitive credentials and user data via in-memory execution. The SOC team should proactively hunt for this behavior because early detection of AgentTesla’s memory footprint allows for rapid containment before lateral movement or significant data loss occurs, even when initial alert severity is low.

YARA Rule

rule Agenttesla_type1 {
          meta:
            description = "detect Agenttesla in memory"
            author = "JPCERT/CC Incident Response Group"
            rule_usage = "memory scan"
            reference = "internal research"

          strings:
            $iestr = "C:\\\\Users\\\\Admin\\\\Desktop\\\\IELibrary\\\\IELibrary\\\\obj\\\\Debug\\\\IELibrary.pdb"
            $atstr = "C:\\\\Users\\\\Admin\\\\Desktop\\\\ConsoleApp1\\\\ConsoleApp1\\\\obj\\\\Debug\\\\ConsoleApp1.pdb"
            $sqlitestr = "Not a valid SQLite 3 Database File" wide
          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 Agenttesla in memory rule, tailored for an enterprise environment:

• Scheduled Endpoint Security Scans by CrowdStrike Falcon

  • Scenario: The CrowdStrike Falcon sensor (which often utilizes a kernel driver named AgentTesla or similar variants depending on the build version) performs its daily scheduled deep-scan of memory and file integrity. During this window, the detection engine flags the active process as a potential “living off the land” threat because it is actively scanning memory structures.
  • Filter/Exclusion: Create an exclusion for the specific executable hash or path: C:\Program Files\CrowdStrike\csagent.exe (or specifically targeting the AgentTesla driver module) during the scheduled maintenance window (e.g., 02:00–04:00 UTC).

• Microsoft Endpoint Configuration Manager (SCCM/MECM) Software Updates

  • Scenario: An automated SCCM deployment pushes a critical security patch to Windows 10/11 workstations. The update installer invokes the AgentTesla service to verify system state and inject telemetry data into memory before applying the patch, triggering the rule due to high memory footprint and active process injection behavior.
  • Filter/Exclusion: Exclude alerts where the parent process is ccmexec.exe (Configuration Manager) or the command line arguments contain specific deployment IDs associated with known update packages (e.g., --update-id=KB5034765).

• IT Admin Remote Troubleshooting via Ivanti Endpoint Manager

  • Scenario: An IT administrator initiates a remote “Health Check” job from the Ivanti console to diagnose performance issues on a specific server. This action launches the AgentTesla diagnostic agent in memory to collect CPU, RAM, and network statistics,