Detects EquationGroup Tool - April Leak

Hunt Hypothesis

The hypothesis is that the detection of the EquationGroup Tool - April Leak indicates potential adversary use of a sophisticated malware variant associated with advanced persistent threats. A SOC team should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage compromise by threat actors leveraging known malicious tooling.

YARA Rule

rule EquationGroup_Toolset_Apr17_Architouch_Eternalsynergy_Smbtouch {
   meta:
      description = "Detects EquationGroup Tool - April Leak"
      author = "Florian Roth"
      reference = "https://steemit.com/shadowbrokers/@theshadowbrokers/lost-in-translation"
      date = "2017-04-15"
      super_rule = 1
      hash1 = "444979a2387530c8fbbc5ddb075b15d6a4717c3435859955f37ebc0f40a4addc"
      hash2 = "92c6a9e648bfd98bbceea3813ce96c6861487826d6b2c3d462debae73ed25b34"
      hash3 = "108243f61c53f00f8f1adcf67c387a8833f1a2149f063dd9ef29205c90a3c30a"
   strings:
      $s1 = "NtErrorMoreProcessingRequired" fullword ascii
      $s2 = "Command Format Error: Error=%x" fullword ascii
      $s3 = "NtErrorPasswordRestriction" fullword ascii

      $op0 = { 8a 85 58 ff ff ff 88 43 4d }
   condition:
      ( uint16(0) == 0x5a4d and filesize < 600KB and 2 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 4 string patterns in its detection logic.

References

• https://steemit.com/shadowbrokers/@theshadowbrokers/lost-in-translation
• 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 process names or command-line arguments.
  Filter/Exclusion: Exclude processes initiated by schtasks.exe with known maintenance command-line arguments (e.g., /create, /run, /delete).

• Scenario: Microsoft Equation Editor Usage
  Description: The EquationGroup tool may be confused with the legacy Microsoft Equation Editor (eqnedit.exe), which is occasionally used in enterprise environments for document formatting.
  Filter/Exclusion: Exclude processes with the full path C:\Windows\System32\eqnedit.exe or any process with the name eqnedit.exe that is not associated with the EquationGroup tool.

• Scenario: Admin Task Using PowerShell for Log Analysis
  Description: A system administrator may use PowerShell scripts (e.g., powershell.exe) to analyze logs or perform forensic tasks, which could trigger the rule due to similar command-line behavior.
  Filter/Exclusion: Exclude processes where the command-line includes -Command or -File with known admin scripts (e.g., C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe -Command "Get-EventLog").

• Scenario: Antivirus or EDR Tool Scanning
  Description: Antivirus or EDR tools (e.g., msmpeng.exe from Windows Defender, or mcafee.exe) may trigger the rule during a scan due to similar process names or behavior.
  Filter/Exclusion: Exclude processes with known EDR/AV tool names (e.g., msmpeng.exe, mcafee.exe, avgnt.exe) or those running under the LocalSystem account.