APT DeputyDog

Hunt Hypothesis

The APT DeputyDog rule detects potential adversary behavior involving suspicious file artifacts associated with a known threat group, indicating possible initial compromise. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage threats before they escalate.

YARA Rule

rule APT_DeputyDog
{

    meta:
        Author      = "FireEye Labs"
        Date        = "2013/09/21"
        Description = "detects string seen in samples used in 2013-3893 0day attacks"
        Reference   = "https://www.fireeye.com/blog/threat-research/2013/09/operation-deputydog-zero-day-cve-2013-3893-attack-against-japanese-targets.html"

    strings:
        $mz = {4d 5a}
        $a = "DGGYDSYRL"

    condition:
        ($mz at 0) and $a
}

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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Scheduled System Maintenance Task
  Description: A legitimate system maintenance task, such as schtasks.exe running a cleanup job, may trigger the rule due to similar file names or behaviors.
  Filter/Exclusion: Check for ProcessName containing schtasks.exe or TaskName matching known maintenance tasks.

• Scenario: Microsoft Windows Update Installer
  Description: The Windows Update installer (wusa.exe) or related processes may be flagged due to similarities in behavior or file hashes with the APT DeputyDog rule.
  Filter/Exclusion: Filter by ProcessName containing wusa.exe or check for CommandLine containing --quiet or --norestart.

• Scenario: Legitimate Admin Tool Usage
  Description: An administrator using a legitimate tool like PsExec or PSTools to remotely manage systems may trigger the rule due to similar execution patterns.
  Filter/Exclusion: Filter by ProcessName containing PsExec.exe or check for CommandLine containing \\ (UNC path) or -s.

• Scenario: Antivirus Quarantine Process
  Description: Antivirus tools like Kaspersky or Bitdefender may run processes to quarantine or analyze files, which could match the YARA rule’s signature.
  Filter/Exclusion: Check for ProcessName containing KavService.exe, Bitdefender.exe, or avgnt.exe.

• Scenario: Log Collection or Monitoring Job
  Description: A log collection job using tools like Splunk or ELK Stack may trigger the rule due to file creation or execution patterns.
  Filter/Exclusion: Filter by ProcessName containing splunkd.exe, logstash, or fluentd,