keyboy init config section

Hunt Hypothesis

The hypothesis is that the detection rule identifies potential adversary activity involving the configuration of a malicious payload within an init section, which may indicate the presence of a persistence mechanism or payload delivery method. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage adversarial activity that could lead to sustained access or data exfiltration.

YARA Rule

rule keyboy_init_config_section
{

    meta:
        author = "Matt Brooks, @cmatthewbrooks"
        desc = "Matches the Init section where the config is stored"
        date = "2016-08-28"

    condition:
        //MZ header //PE signature //Payloads are normally smaller but the new dropper we spotted //is a bit larger. //Observed virtual sizes of the .Init section vary but they've //always been 1024, 2048, or 4096 bytes.
        uint16(0) == 0x5A4D and uint32(uint32(0x3C)) == 0x00004550 and filesize < 300KB and for any i in (0..pe.number_of_sections - 1): (pe.sections[i].name == ".Init" and pe.sections[i].virtual_size % 1024 == 0)
}

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
• Source Rule

False Positive Guidance

• Scenario: System update or patching tool configuration
  Description: A legitimate system update tool (e.g., Ansible, Puppet, or Chef) may generate configuration files in the same format as the malicious keyboy_init_config_section.
  Filter/Exclusion: Check for known update tools or check the file’s location against standard system directories like /etc/ or /opt/.

• Scenario: Scheduled job configuration using cron or systemd
  Description: A legitimate cron job or systemd service file might contain similar syntax to the malicious configuration section, especially if it includes environment variables or init scripts.
  Filter/Exclusion: Filter by file extensions (e.g., .cron, .service) or check the file path against known cron/systemd directories like /etc/cron.d/ or /etc/systemd/system/.

• Scenario: Configuration of a legitimate init system (e.g., systemd, sysvinit)
  Description: A system administrator may manually edit init scripts or configuration files (e.g., /etc/init.d/ or /lib/systemd/system/) which could resemble the malicious pattern.
  Filter/Exclusion: Check for known init system files or use a file type filter (e.g., file: /etc/init.d/ or file: /lib/systemd/system/).

• Scenario: Configuration of a legitimate container orchestration tool (e.g., Docker, Kubernetes)
  Description: Docker or Kubernetes configuration files (e.g., docker-compose.yml, k8s.yaml) may contain similar syntax that matches the YARA rule.
  Filter/Exclusion: Filter by file extensions (e.g., .yml, .yaml) or check the file path against known container directories like /etc/docker/ or /var/lib/kubelet/.

• Scenario: Configuration of a legitimate log management tool (e.g