Detects EquationGroup Tool - April Leak

Hunt Hypothesis

The hypothesis is that the detection of EquationGroup Tool - April Leak indicates potential adversary use of a sophisticated, legacy malware family that may be used for long-term persistence or data exfiltration. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate potential advanced persistent threats that may have evaded traditional detection methods.

YARA Rule

rule EquationGroup_Toolset_Apr17_AdUser_Implant {
   meta:
      description = "Detects EquationGroup Tool - April Leak"
      author = "Florian Roth"
      reference = "https://steemit.com/shadowbrokers/@theshadowbrokers/lost-in-translation"
      date = "2017-04-15"
      hash1 = "fd2efb226969bc82e2e38769a10a8a751138db69f4594a8de4b3c0522d4d885f"
   strings:
      $s1 = ".?AVFeFinallyFailure@@" fullword ascii
      $s2 = "(&(objectCategory=person)(objectClass=user)(cn=" fullword wide
   condition:
      ( uint16(0) == 0x5a4d and filesize < 40KB and 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 2 string patterns in its detection logic.

References

• https://steemit.com/shadowbrokers/@theshadowbrokers/lost-in-translation
• Source Rule

False Positive Guidance

• Scenario: Legitimate system update using msiexec.exe
  Filter/Exclusion: process.name == "msiexec.exe" && process.args contains "update"

• Scenario: Scheduled backup job using vssadmin.exe
  Filter/Exclusion: process.name == "vssadmin.exe" && process.args contains "backup"

• Scenario: Admin task using taskkill.exe to terminate a non-malicious process
  Filter/Exclusion: process.name == "taskkill.exe" && process.args contains "/F /PID"

• Scenario: PowerShell script running a legitimate configuration task using powershell.exe
  Filter/Exclusion: process.name == "powershell.exe" && process.args contains "Configure-System.ps1"

• Scenario: Antivirus scan using msmpeng.exe (Microsoft Antivirus engine)
  Filter/Exclusion: process.name == "msmpeng.exe" && process.args contains "Scan"