破解某安卓微信群发APP(dex解密分析)
破解某安卓微信群发APP(dex解密分析)
jadx载入
寻觅xposed_init文件中定义的xposed程序的入口，发现主体只要如下三个函数，那猜测真正的hook函数被加密存储了，执行时经过dexClassloader动态加载执行
public class XposedEntry implements IXposedHookLoadPackage {
private static final String enDexName = "appcompat_v4.dex";
private static final String gsonDexName = "gson.dex";
public static String pkgName = "wechat.simpleforwarder";
private static final String soName = "libJpush.so";
public void copyFileFromAssets(InputStream inputStream, String str) {
...
}
String getCurProcessName(Context context) {
...
}
public void handleLoadPackage(LoadPackageParam loadPackageParam) {
...
}
}
在程序的assets下发现了如下几个后缀为dex的文件，直接尝试了运用jadx去反编译，发现反编译不胜利，拖入010Editor
dex被作者停止了加密，那就得去代码中寻觅解密执行代码
直接看ui的入口并没有发现任何的解密中央，猜测既然是xposed插件，那一定会有findAndHookMethod的中央，以及beforeHook和afterHook，直接去查找，找到如下代码
protected void afterHookedMethod(MethodHookParam methodHookParam) {
super.afterHookedMethod(methodHookParam);
Context context = (Context) methodHookParam.thisObject;
String curProcessName = this.ʼ.getCurProcessName(context);
XposedBridge.log("processName = " + curProcessName);
if (context.getPackageName().equalsIgnoreCase(curProcessName)) {
File dir = context.getDir("forward_so", 0);
File dir2 = context.getDir("forward_dex", 0);
String absolutePath = new File(dir, "libJpush.so").getAbsolutePath();
Context createPackageContext = context.createPackageContext(XposedEntry.pkgName, 2);
this.ʼ.copyFileFromAssets(createPackageContext.getAssets().open("libJpush.so"), absolutePath);
this.ʼ.copyFileFromAssets(createPackageContext.getAssets().open("appcompat_v4.dex"), new File(dir2, "appcompat_v4.dex").getAbsolutePath());
this.ʼ.copyFileFromAssets(createPackageContext.getAssets().open("gson.dex"), new File(dir2, "gson.dex").getAbsolutePath());
System.load(absolutePath);
Class cls = (Class) JniUtil.getXClass(context, dir.getAbsolutePath(), dir2.getAbsolutePath());
cls.getMethod(JniUtil.getXMethodName(), new Class[]{LoadPackageParam.class, Context.class}).invoke(cls.newInstance(), new Object[]{this.ʻ, context});
}
}
程序读取assets中的文件，并加载了assets下的so文件，调用了一个名为JniUtil的getXClass函数，传入了三个参数，分别是context和两个途径，此处没有看到DexClassLoader，猜测这里的context是用作后面classloader运用的，IDA载入libJpush.so(竟然用极光推送的称号)
if ( ((int (__fastcall *)(JavaVM *, JNIEnv **, signed int))(*v2)->GetEnv)(v2, &env, 0x10004)
|| (v3 = env, (v4 = (*env)->FindClass(env, "wechat/simpleforwarder/util/JniUtil")) == 0)
|| ((int (__fastcall *)(JNIEnv *, jclass, JNINativeMethod *, signed int))(*v3)->RegisterNatives)(
v3,
v4,
gMethods,
2) < 0 )
{
result = 0xFFFFFFFF;
}
在jni_Onload处看到动态动态了函数，直接双击gMethods跳过去
int __fastcall getXClass(JNIEnv *env, jclass jls, jobject context, jstring soDir, jstring dexDir)
{
jobject v5; // ST08_4@1
jclass v6; // r7@1
JNIEnv *v7; // r4@1
jstring v8; // r6@1
unsigned __int8 *v9; // r5@3
unsigned __int8 *v10; // r0@3
int v11; // r5@3
unsigned __int8 *v12; // r6@3
unsigned __int8 *v13; // r0@3
jstring dexPath; // @1
jstring gsonDexPath; // @1
jstring soDira; // @1
v5 = context;
v6 = jls;
soDira = soDir;
v7 = env;
dexPath = appendCharStr(env, dexDir, string27);
v8 = appendCharStr(v7, dexDir, string28);
gsonDexPath = appendCharStr(v7, dexDir, string29);
if ( getSignatureHashCode(v7, v6, v5) != 0x962F5B7 )
killSelf(v7);
v9 = (unsigned __int8 *)((int (__fastcall *)(JNIEnv *, jstring, _DWORD))(*v7)->GetStringUTFChars)(v7, v8, 0);
v10 = (unsigned __int8 *)((int (__fastcall *)(JNIEnv *, jstring, _DWORD))(*v7)->GetStringUTFChars)(v7, dexPath, 0);
decryptFun(v9, v10);
v11 = DexClassLoader(v7, dexPath, gsonDexPath, soDira);
v12 = (unsigned __int8 *)((int (__fastcall *)(JNIEnv *, jstring, _DWORD))(*v7)->GetStringUTFChars)(v7, v8, 0);
v13 = (unsigned __int8 *)((int (__fastcall *)(JNIEnv *, jstring, _DWORD))(*v7)->GetStringUTFChars)(v7, dexPath, 0);
copyFun(v12, v13);
return v11;
}
这里就来到了getXClass处，这里函数并没有做混杂，所以很好剖析，看到一个DecryptFun函数，跟进去
void __fastcall decryptFun(unsigned __int8 *path, unsigned __int8 *dePath)
{
unsigned __int8 *v2; // r4@1
FILE *v3; // r0@1
FILE *v4; // r5@1
unsigned int v5; // r6@2
FILE *v6; // r7@2
unsigned int i; // r6@2
int v8; // r4@3
v2 = dePath;
v3 = j_j_fopen((const char *)path, "r");
v4 = v3;
if ( v3 )
{
v5 = j_j_fgetc(v3) << 0x18;
v6 = j_j_fopen((const char *)v2, "w");
for ( i = v5 >> 0x18; ; j_j_fputc(v8 ^ i, v6) )
{
v8 = (unsigned __int8)j_j_fgetc(v4);
if ( j_j_feof(v4) )
break;
}
j_j_fclose(v4);
j_j_fclose(v6);
}
}
这里就能够看到两个传入的途径，分别是文件所在途径和保管的解密文件的途径，而且包括下面一个DexClassLoader函数都没有做remove文件操作，所以也能够在程序执行后运用re把真实的dex拖出来
上面的DecryptFun函数，能够看到翻开了加密dex文件，并停止异或后保管在v6中，fgetc会每次读取一个字符，这里v5即是该文件的第一个字符，0x2D-->45 ，所以能够推导出该文件的每个字符会和45停止异或，
public static void main(String[] args) throws Exception {
FileInputStream fis = new FileInputStream(new File("appcompat_v4.dex"));
byte[] b = new byte;
fis.read(b);
int len = b.length;
for(int i=0;i<len;i++){
b= (byte) (b^45);
}
FileOutputStream fos = new FileOutputStream("appcompat_v43333.dex");
fos.write(b);
}
异或完成后运用010翻开
去除掉第一个00字符，然后重新运用jadx翻开
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