X-Agent/CHOPSTICK Implant by APT28

Hunt Hypothesis

The X-Agent/CHOPSTICK Implant by APT28 is a high-impact adversary behavior indicating a persistent, stealthy compromise used by a sophisticated threat group to maintain long-term access and exfiltrate data. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect and mitigate advanced persistent threats before significant data loss or system disruption occurs.

YARA Rule

rule IMPLANT_3_v3 {
   meta:
      description = "X-Agent/CHOPSTICK Implant by APT28"
      author = "US CERT"
      reference = "https://www.us-cert.gov/ncas/current-activity/2017/02/10/Enhanced-Analysis-GRIZZLY-STEPPE"
      date = "2017-02-10"
      score = 85
   strings:
      $STR1 = ".?AVAgentKernel@@"
      $STR2 = ".?AVIAgentModule@@"
      $STR3 = "AgentKernel"
   condition:
      (uint16(0) == 0x5A4D or uint16(0) == 0xCFD0 or uint16(0) == 0xC3D4 or
      uint32(0) == 0x46445025 or uint32(1) == 0x6674725C) and any 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

False Positive Guidance

Scenario: Legitimate scheduled job running chopsticks.exe as part of a system maintenance task
Filter/Exclusion: process.parent_process_name == "Task Scheduler" or process.command_line contains "schtasks.exe"
Scenario: System update or patching process using chopsticks.exe as a dependency
Filter/Exclusion: process.parent_process_name == "Windows Update" or process.command_line contains "wuauclt.exe"
Scenario: Admin using chopsticks.exe for legitimate forensic analysis or incident response
Filter/Exclusion: process.user == "Domain\Administrator" and process.command_line contains "analyze.exe" or "forensic_tool.exe"
Scenario: Malicious file named chopsticks.exe but not related to APT28 (false positive due to name similarity)
Filter/Exclusion: file.hash.sha256 == "known_legitimate_chopsticks_hash" or file.name != "chopsticks.exe"
Scenario: Legitimate third-party tool named chopsticks.exe used for system monitoring
Filter/Exclusion: process.parent_process_name == "System Center Operations Manager" or process.command_line contains "SCOM.exe"