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deobfuscator.go
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/
deobfuscator.go
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package main
import (
"bufio"
"fmt"
"io"
"net/http"
"os"
"os/exec"
"regexp"
"strconv"
"strings"
)
// Auto de-obfuscation of gameforge "game1.js" fingerprint script
// https://gameforge.com/tra/game1.js
//
// You need `node` and `js-beautify` to be installed and available.
func main() {
content := getGame1Js()
raw := extractRawJavascript(content)
// Step1 is to unescape the string using node, then run js-beautify on it.
// Once done, we replace some trivial obfuscation patterns.
// Code should be more or less readable at this point
step1 := nodeUnescape(raw)
step1 = jsBeautify(step1)
step1 = replaceTrivial(step1)
step1 = replaceDecodeStrRefs(step1)
// Start node and feed initial source code
srcForNode := strings.ReplaceAll(step1, "\n", "")
cmd, writer, scanner := startNodeProcess()
defer cmd.Process.Kill()
_ = sendJavaScript(writer, scanner, srcForNode)
step1 = replaceObfuscatedStrings(step1, writer, scanner)
step1 = replaceHexNumbers(step1)
_ = os.WriteFile("out.js", []byte(step1), 0644)
}
// Get game1.js from gameforge, or read it from disk if it is already downloaded
func getGame1Js() (out string) {
fileName := "game1.js"
if _, err := os.Stat(fileName); err != nil {
fmt.Println("downloading " + fileName)
res, err := http.Get("https://gameforge.com/tra/game1.js")
if err != nil {
panic(err)
}
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
if err := os.WriteFile(fileName, body, 0644); err != nil {
panic(err)
}
out = string(body)
} else {
fmt.Println(fileName + " exists")
content, err := os.ReadFile(fileName)
if err != nil {
panic(err)
}
out = string(content)
}
return
}
// game1.js eval a string, this function extract that string
func extractRawJavascript(src string) string {
firstIdx := strings.Index(src, "'")
lastIdx := strings.LastIndex(src, "'")
return src[firstIdx+1 : lastIdx]
}
// replaceTrivial replace some trivial "obfuscations"
func replaceTrivial(in string) string {
in = strings.ReplaceAll(in, "!![]", "true")
in = strings.ReplaceAll(in, "![]", "false")
in = strings.ReplaceAll(in, `\x20`, ` `)
in = strings.ReplaceAll(in, `\x22`, `"`)
return in
}
func replaceDecodeStrRefs(in string) string {
// First line contains the function to decode a string
// const decodeStrRef = decodeStr;
scanner := bufio.NewScanner(strings.NewReader(in))
scanner.Scan()
rgx := regexp.MustCompile(`const (\w+) = (\w+);`)
m := rgx.FindStringSubmatch(scanner.Text())
in = strings.ReplaceAll(in, m[1], "decodeStrRef")
in = strings.ReplaceAll(in, m[2], "decodeStr")
// Replace all references to the decodeStr function
for { // repeat until no more matches
rgx = regexp.MustCompile(`const (\w+) = decodeStr`)
m1 := rgx.FindAllStringSubmatch(in, -1)
count := 0
for _, m := range m1 {
if m[1] != "decodeStrRef" {
in = strings.ReplaceAll(in, m[1], "decodeStrRef")
count++
}
}
if count == 0 {
break
}
}
return in
}
// Decode and replace all obfuscated strings
func replaceObfuscatedStrings(in string, writer *bufio.Writer, scanner *bufio.Scanner) string {
rgx := regexp.MustCompile(`(decodeStrRef\(([^)]+)\))`)
matches := rgx.FindAllStringSubmatch(in, -1)
for _, match := range matches {
code := fmt.Sprintf("decodeStr(%s);", match[2])
newVal := sendJavaScript(writer, scanner, code)
in = strings.Replace(in, match[1], newVal, 1)
}
return in
}
// Replace all base 16 numbers back to base 10
func replaceHexNumbers(in string) string {
replacementFunc := func(s string) string {
v, _ := strconv.ParseInt(s[2:], 16, 64)
return strconv.FormatInt(v, 10)
}
re := regexp.MustCompile(`\b0x[0-9a-fA-F]+\b`)
in = re.ReplaceAllStringFunc(in, replacementFunc)
return in
}
// Start node in interactive mode.
// The script will then use this process to "decrypt" the strings in the obfuscated javascript and replace them.
func startNodeProcess() (*exec.Cmd, *bufio.Writer, *bufio.Scanner) {
cmd := exec.Command("node", "--interactive")
stdin, err := cmd.StdinPipe()
if err != nil {
panic(err)
}
stdout, err := cmd.StdoutPipe()
if err != nil {
panic(err)
}
if err := cmd.Start(); err != nil {
panic(err)
}
writer := bufio.NewWriter(stdin)
scanner := bufio.NewScanner(stdout)
scanner.Scan()
scanner.Scan()
return cmd, writer, scanner
}
// Send some javascript to the node process and return the output from node.
func sendJavaScript(writer *bufio.Writer, scanner *bufio.Scanner, code string) string {
codeWithNewline := code + "\n"
_, err := writer.WriteString(codeWithNewline)
if err != nil {
panic(err)
}
if err := writer.Flush(); err != nil {
panic(err)
}
if scanner.Scan() {
return strings.TrimPrefix(scanner.Text(), "> ")
}
if scanner.Err() != nil {
panic(err)
}
return ""
}
// Run "unescape" using node
func nodeUnescape(in string) string {
cmd := exec.Command("node", "-e", "console.log(unescape('"+in+"'))")
processed, err := cmd.Output()
if err != nil {
panic(err)
}
return string(processed)
}
// Run js-beautify to format the javascript into human-readable code
func jsBeautify(in string) string {
cmd := exec.Command("js-beautify", "-q", "-f '-'")
cmd.Stdin = strings.NewReader(in)
processed, err := cmd.Output()
if err != nil {
panic(err)
}
return string(processed)
}