BlackEnergy DDoS Bot Crypter additional

Hunt Hypothesis

This rule identifies the presence of the BlackEnergy DDoS bot crypter, a component used to encrypt and obfuscate the botnet’s payload to evade signature-based detection. Proactively hunting for this artifact in Azure Sentinel allows the SOC to uncover dormant or hidden botnet infrastructure before it is activated to launch volumetric attacks against cloud resources.

YARA Rule

rule BlackEnergy_DDoS_Bot_Crypter_additional: PEiD
{
    strings:
        $a = { 55 ?? ?? 81 EC 1C 01 00 00 53 56 57 6A 04 BE 00 30 00 00 56 FF 35 00 20 11 13 6A 00 E8 ?? 03 00 00 ?? ?? 83 C4 10 ?? FF 89 7D F4 0F }
    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 software development team uses a custom C++ wrapper or a tool like UPX (Ultimate Packer for eXecutables) to compress and obfuscate a small utility or plugin before deployment. The specific compression algorithm or header structure may match the byte patterns defined in the “additional” crypter rule, triggering a false positive on legitimate, signed binaries.

  • Filter/Exclusion: Exclude files located in specific development build directories (e.g., C:\Builds\, C:\Artifacts\) or exclude processes where the parent is a known compiler or packer (e.g., msbuild.exe, upx.exe) and the file has a valid digital signature from the organization’s code-signing certificate.

• Scenario: An IT operations team deploys a proprietary, internally developed PowerShell script or .NET assembly that uses a custom encryption layer for configuration files or embedded resources. If the internal crypter uses a standard XOR or AES implementation with a specific key size or header that overlaps with the BlackEnergy crypter’s signature, the rule may flag these internal tools during routine maintenance or scheduled task execution.

  • Filter/Exclusion: Exclude files with extensions .ps1, .dll, or .exe that are located in the C:\Program Files\InternalTools\ directory and are owned by the Domain Admins or IT_Ops group. Additionally, exclude if the file’s SHA256 hash is present in a trusted internal artifact registry.

• Scenario: A security team runs a periodic integrity check using a tool like ssdeep or a custom hash-based comparator that reads and processes executable files in memory or on disk. If the tool itself is a small, obfuscated binary (common for security utilities to avoid detection) or if it temporarily writes a decrypted/expanded version of a target file to a temp directory