Stones PE Encruptor v113

Hunt Hypothesis

This hypothesis targets the presence of the Stones PE Encryptor, a tool frequently used by adversaries to obfuscate malicious payloads and evade static analysis during the initial stages of an intrusion. Proactively hunting for this specific encryptor in Azure Sentinel allows the SOC to identify compromised endpoints or suspicious artifacts before the encrypted payload is decrypted and executed, reducing the mean time to detection for stealthy malware campaigns.

YARA Rule

rule Stones_PE_Encruptor_v113: PEiD
{
    strings:
        $a = { 55 57 56 52 51 53 E8 ?? ?? ?? ?? 5D 8B D5 81 }
    condition:
        $a at pe.entry_point

}

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 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: A development team uses the Stones PE Encruptor to obfuscate proprietary C# or C++ executables for internal testing or to protect intellectual property before deployment to non-production environments.
  • Filter/Exclusion: Exclude processes where the parent process is a known IDE or build tool (e.g., devenv.exe, msbuild.exe, dotnet.exe) and the file path resides within standard development directories (e.g., C:\Projects\, C:\Builds\, C:\Users\<dev_user>\Source\).
• Scenario: An IT operations team runs a scheduled PowerShell job to encrypt legacy .NET applications that must be run on older Windows versions but are being temporarily obfuscated to prevent reverse engineering during a migration phase.
  • Filter/Exclusion: Exclude events where the process name is powershell.exe or pwsh.exe and the command line contains specific keywords like -Encrypt or -Obfuscate, or where the working directory matches the scheduled task’s designated output folder (e.g., C:\ITOps\Migration\EncryptedApps\).
• Scenario: A security engineering team performs a “red team” exercise or a controlled chaos engineering test where they intentionally deploy a known benign PE file encrypted with Stones PE Encryptor to validate detection coverage in a sandboxed environment.
  • Filter/Exclusion: Exclude hosts tagged with a specific AD group or Azure Tag (e.g., Tag: "Sandbox", Tag: "RedTeam") or exclude processes running under a dedicated service account (e.g., svc_redteam) that is not used for regular application execution.
• Scenario: A third-party vendor provides a custom utility tool that has been pre-encrypted with Stones PE Encryptor to protect their licensing mechanism, and this tool is installed in a