Detects ELF obfuscation technique used by Sindoor dropper related to APT 36

Hunt Hypothesis

This hunt hypothesis targets adversaries employing ELF file obfuscation, a signature behavior of the Sindoor dropper associated with APT 36, to identify stealthy initial access attempts that may evade standard signature-based detection. Proactively hunting for this technique in Azure Sentinel is critical because it enables the SOC team to uncover sophisticated evasion tactics early, preventing potential lateral movement and data exfiltration before the threat fully establishes a foothold within the environment.

YARA Rule

rule SUSP_LNX_Sindoor_DesktopFile_Aug25 {
   meta:
      description = "Detects ELF obfuscation technique used by Sindoor dropper related to APT 36"
      author = "Pezier Pierre-Henri"
      date = "2025-08-29"
      score = 70
      reference = "Internal Research"
      hash = "9943bdf1b2a37434054b14a1a56a8e67aaa6a8b733ca785017d3ed8c1173ac59"
      id = "16719116-0cb2-5c70-a86f-f65f9ea32153"
   strings:
      $hdr = "[Desktop Entry]"
      $s1 = "printf '\\\\x7FELF' | dd of"
      $s2 = "Future_Note_Warfare_OpSindoor.pdf"
   condition:
      filesize < 100KB
      and $hdr
      and any of ($s*)
}

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 5 specific false positive scenarios for the “Detects ELF obfuscation technique used by Sindoor dropper related to APT 36” rule, including suggested filters and exclusions:

• Scenario: Legitimate Software Deployment via SCCM/Intune

  • Context: System Center Configuration Manager (SCCM) or Microsoft Intune agents frequently deploy obfuscated ELF binaries (e.g., updated Adobe Acrobat readers or Java JREs) to endpoints. The deployment process often involves the ccmsetup.exe or intunagent.exe creating temporary, packed ELF files that mimic the Sindoor dropper’s structure.
  • Filter/Exclusion: Exclude processes where the parent executable is ccmsetup.exe, Microsoft.IntuneManagementAgent.exe, or wsmantrc.exe. Additionally, filter out events where the file hash matches known good hashes in your CMDB (Configuration Management Database) for standard enterprise software versions.

• Scenario: Automated Backup and Archiving Jobs

  • Context: Enterprise backup solutions like Veeam Backup & Replication or Commvault often utilize obfuscated ELF agents to compress and package data before transmission. These agents may spawn child processes that perform on-the-fly obfuscation of temporary archive containers, triggering the detection logic due to similar entropy levels in the binary header.
  • Filter/Exclusion: Create an exclusion for scheduled tasks running under specific service accounts (e.g., VeeamBackupService, CommvaultAgent) during defined maintenance windows (e.g., 02:00–04:00). Filter based on the command line arguments containing keywords like “archive,” “backup,” or “.vbk” extensions.

• Scenario: Development and CI/CD Pipeline Artifacts

  • Context: In environments with internal DevOps teams, Jenkins, GitLab Run