某单机手游完整性校验分析
本帖最后由 bags 于 2023-11-2 23:52 编辑#### 前言
只是普通的单机手游，广告比较多，所以分析处理了下，校验流程蛮有意思的，所以就分享出来了
#### 1.重打包崩溃处理
样本进行了加固，对其dump出dex后重打包出现崩溃
ida分析地址发现为jni函数引起
利用Xposed直接替换该函数，崩溃问题解决
```java
XposedHelpers.findAndHookMethod("com.unity3d.player.UnityPlayerActivity", classLoader, "IsHDR_DisplayBoot", java.lang.String.class, java.lang.String.class, new XC_MethodReplacement() {
@Override
protected Object replaceHookedMethod(MethodHookParam methodHookParam) throws Throwable {
return null;
}
});
```
#### 2.卡加载界面处理
但是出现了新的问题，游戏卡在了加载页面
对该类的其他jni函数进行分析，发现supportVulkan很明显进行了签名读取，对其去除签名校验。
此处参考项目：**(https://github.com/L-JINBIN/ApkSignatureKillerEx)**
#### 3.地图无法进入问题分析（基于原包）
去除完签名校验后，游戏能正常进入主页面，但是点击游戏地图没有任何反应。
在对原包进行多次测试发现，在首次启动游戏时，如果断网也会出现无法正常进入地图的问题，怀疑是游戏首次启动进行了网络请求进行数据校验
经过抓包对比定位到可疑数据包
利用Frida的算法通杀脚本没有定位到相关内容，怀疑是so层进行了请求
##### 3.1 hook send函数进行调用栈分析
通过调用栈可以很清晰看到请求是从unity引擎相关的so中发出的。
##### 3.2 il2cppTrace对请求调用栈分析
查阅资料，在unity中，网络请求主要通过`UnityWebRequest` 类来执行网络请求，利用(https://github.com/vfsfitvnm/frida-il2cpp-bridge)对UnityWebRequest进行trace，打印调用栈得
```js
0x0247db9c ┌─UnityEngine.Networking.UnityWebRequest::.ctor(this = UnityEngine.Networking.UnityWebRequest, url = "http://106.54.194.167:8077/CheckUpdate", method = "POST")
0x0247db00 │ ┌─UnityEngine.Networking.UnityWebRequest::set_url(this = UnityEngine.Networking.UnityWebRequest, value = "http://106.54.194.167:8077/CheckUpdate")
0x0247ef38 │ │ ┌─UnityEngine.Networking.UnityWebRequest::InternalSetUrl(this = UnityEngine.Networking.UnityWebRequest, url = "http://106.54.194.167:8077/CheckUpdate")
0x0247ef38 │ │ └─UnityEngine.Networking.UnityWebRequest::InternalSetUrl
0x0247db00 │ └─UnityEngine.Networking.UnityWebRequest::set_url
0x0247dc1c │ ┌─UnityEngine.Networking.UnityWebRequest::set_method(this = UnityEngine.Networking.UnityWebRequest, value = "POST")
0x0247e4e0 │ │ ┌─UnityEngine.Networking.UnityWebRequest::InternalSetMethod(this = UnityEngine.Networking.UnityWebRequest, methodType = Post)
0x0247e4e0 │ │ └─UnityEngine.Networking.UnityWebRequest::InternalSetMethod
0x0247dc1c │ └─UnityEngine.Networking.UnityWebRequest::set_method
0x0247db9c └─UnityEngine.Networking.UnityWebRequest::.ctor
```
在IDA中进行交叉引用分析定位到UnitySDKManager类
```
追踪调用定位到
class UnitySDK.UnitySDKManager.<PostData>d__25 : System.Object, System.Collections.Generic.IEnumerator<System.Object>, System.Collections.IEnumerator, System.IDisposable
private Boolean MoveNext() { }
```
增加UnitySDKManager类重新对其trace（因为出现报错，把参数输出关了）
```
0x00b15b44 ┌─UnitySDK.UnitySDKManager::ServerVerifyApk
0x00b04b3c │ ┌─UnitySDK.UnitySDKManager::GetFileInfoList
0x00b04b3c │ └─UnitySDK.UnitySDKManager::GetFileInfoList
0x00b06ec0 │ ┌─UnitySDK.UnitySDKManager::GetGamePackageName
0x00b06ec0 │ └─UnitySDK.UnitySDKManager::GetGamePackageName
0x00b06204 │ ┌─UnitySDK.UnitySDKManager::GetSDKVersion
0x00b06204 │ └─UnitySDK.UnitySDKManager::GetSDKVersion
0x00b06278 │ ┌─UnitySDK.UnitySDKManager::HexStringToHex
0x00b06278 │ └─UnitySDK.UnitySDKManager::HexStringToHex
0x00b10fcc │ ┌─UnitySDK.UnitySDKManager::EncryptString
0x00b10fcc │ └─UnitySDK.UnitySDKManager::EncryptString
0x00b100a4 │ ┌─UnitySDK.UnitySDKManager::PostData
0x00a341fc │ │ ┌─UnitySDK.UnitySDKManager.<PostData>d__25::.ctor
0x00a341fc │ │ └─UnitySDK.UnitySDKManager.<PostData>d__25::.ctor
0x00b100a4 │ └─UnitySDK.UnitySDKManager::PostData
0x00a3422c │ ┌─UnitySDK.UnitySDKManager.<PostData>d__25::MoveNext
0x00b12be4 │ │ ┌─UnitySDK.UnitySDKManager::GetUrl
0x00b12be4 │ │ └─UnitySDK.UnitySDKManager::GetUrl
0x0247db9c │ │ ┌─UnityEngine.Networking.UnityWebRequest::.ctor
0x0247db00 │ │ │ ┌─UnityEngine.Networking.UnityWebRequest::set_url
0x0247ef38 │ │ │ │ ┌─UnityEngine.Networking.UnityWebRequest::InternalSetUrl
0x0247ef38 │ │ │ │ └─UnityEngine.Networking.UnityWebRequest::InternalSetUrl
0x0247db00 │ │ │ └─UnityEngine.Networking.UnityWebRequest::set_url
0x0247dc1c │ │ │ ┌─UnityEngine.Networking.UnityWebRequest::set_method
0x0247e4e0 │ │ │ │ ┌─UnityEngine.Networking.UnityWebRequest::InternalSetMethod
0x0247e4e0 │ │ │ │ └─UnityEngine.Networking.UnityWebRequest::InternalSetMethod
0x0247dc1c │ │ │ └─UnityEngine.Networking.UnityWebRequest::set_method
0x0247db9c │ │ └─UnityEngine.Networking.UnityWebRequest::.ctor
0x0247e0f4 │ │ ┌─UnityEngine.Networking.UnityWebRequest::set_uploadHandler
0x0247e0f4 │ │ └─UnityEngine.Networking.UnityWebRequest::set_uploadHandler
0x0247dfdc │ │ ┌─UnityEngine.Networking.UnityWebRequest::set_downloadHandler
0x0247dfdc │ │ └─UnityEngine.Networking.UnityWebRequest::set_downloadHandler
0x0247f66c │ │ ┌─UnityEngine.Networking.UnityWebRequest::SetRequestHeader
0x0247f66c │ │ └─UnityEngine.Networking.UnityWebRequest::SetRequestHeader
0x0247e42c │ │ ┌─UnityEngine.Networking.UnityWebRequest::Send
0x0247e430 │ │ │ ┌─UnityEngine.Networking.UnityWebRequest::SendWebRequest
0x0247e42c │ │ │ └─UnityEngine.Networking.UnityWebRequest::Send
0x0247e430 │ │ └─UnityEngine.Networking.UnityWebRequest::SendWebRequest
0x00a3422c │ └─UnitySDK.UnitySDKManager.<PostData>d__25::MoveNext
0x00a34cd4 │ ┌─UnitySDK.UnitySDKManager.<PostData>d__25::System.Collections.IEnumerator.get_Current
0x00a34cd4 │ └─UnitySDK.UnitySDKManager.<PostData>d__25::System.Collections.IEnumerator.get_Current
0x00b15b44 └─UnitySDK.UnitySDKManager::ServerVerifyApk
```
通过调用栈可以初步对校验流程进行了解，主要通过ServerVerifyApk函数进行校验，经过一系列字符串加解密，最后进行网络请求
##### 3.3 加解密函数hook分析
对关键函数进行hook分析
```
0x00b10fcc │ UnitySDK.UnitySDKManager::EncryptString
0x00b0b13c │ UnitySDK.UnitySDKManager::DecryptString
il2cpp: EncryptString:"{"appid":"com.meta.peopleground.dream","appName":"com.meta.peopleground.dream","appVer":"1.0.1","sdkVer":"2","appFileList":"981lDpbOb+vjRn/3yI74fI+1S5cr08qKLGq0xg7TcfFOA7hRePAQjXPCgIzEC+p58RThRtl4PIsPEgiJZVYn1e2oZl06jeKGD6+C0Zy6lQaDiAVaOtO5szilZxfmN2j8XtlBmBaOzOVBBi6ctJamGsfM2XbkGqYtf/TlNyvOZ8p5YDdOgnhG+WonkjG1sGEbuqc4sm+hkCxOC7dX1rEM4/5S6wT1erPL5+iWJoRpiTuHok15zCQjdNFCXn97Vwg+/h8eXrtxrDvkkLqqCff2D0WrAISmIOi4fY97ulhpz5Pey2vJlkLK5MdSApENx4exv3t4Q1sVfoPojwDueXAW9T1RTOc1LeK0cYMrBjsE1W8="}"
il2cpp: EncryptString result:"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"
il2cpp: DecryptString:"+CVWCEji2Lgf4nUTWb7J/Q=="
il2cpp: DecryptString result:"100"
```
发现之前抓包获得的请求体相对应，其中，appFileList还是密文，继续分析
##### 3.4 追EncryptString函数
与dump.cs中的函数进行对照发现v14 由字符串转hex转base64获得
```
System.Byte[] HexStringToHex(System.String inputHex); // 0x00b06278
```
hook HexStringToHex 函数获得参数
```
il2cpp: inputHex:"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"
```
IDA继续查找调用发现其中字符串由GetFileInfoList函数获得
```c
// static System.IntPtr GetFileInfoList(); // 0x00b04b3c
__int64 sub_B04B3C()
{
__int64 (*v0)(void); // x8
__int64 v2; // BYREF
int v3; //
char v4; //
v0 = (__int64 (*)(void))qword_30365A0;
if ( !qword_30365A0 )
{
v3 = 0;
v2 = (__int64)"UnitySDK";
v2 = 8LL;
v2 = (__int64)"GetFileInfoList";
v2 = 15LL;
v2 = 0x200000000LL;
v4 = 0;
v0 = (__int64 (*)(void))sub_812FB4(v2);
qword_30365A0 = (__int64)v0;
}
return v0();
}
```
很明显，调用了libUnitySDK.so中的GetFileInfoList函数获得
##### 3.5 libUnitySDK.so分析
```c
__int64 GetFileInfoList()
{
return FileInfoListStr;
}
```
FileInfoListStr在writeFileJson函数中被赋值，而writeFileJson则是由java函数上文中的IsHDR_DisplayBoot调用（该函数首个参数为base.apk路径）
很明显，ll11l1l1ll函数 对之前的明文字符串进行了加密，frida hook打印参数
```
args: {
"HashList" :
{
"AndroidManifest.xml" : " c72b1d2",
"assets/bin/Data/Managed/Metadata/game.dat" : "a34a757d",
"classes.dex" : "58b6cf21",
"lib/arm64-v8a/libUnitySDK.so" : "b56d5af4",
"lib/armeabi-v7a/libUnitySDK.so" : "3d548ba2"
},
"fileCount" : 1620
}
returnResult: 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
```
至此，除了具体的字符串加密算法，游戏的校验流程已经很清晰
#### 4.校验流程归纳
+ 签名校验
+ 读取base.apk进行关键文件crc读取
+ 进行服务器请求，对关键文件crc校验
#### 5.后记
对该校验去除的思路：
+ 对读取安装包的函数 zip_open 或java层的 IsHDR_DisplayBoot 函数进行hook，进行参数替换，进行io重定向
+ 基于il2cpp中的ServerVerifyApk函数进行更详细的分析，直接对其检测去除
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样本链接：https://pan.baidu.com/s/1awWYCF2nT50qPRj8_CRt-A?pwd=d8wn 大佬牛逼! 感谢分享，论坛支持md格式，可以优化下 感谢分享！ 看不懂，但是很震撼 术业有专攻，厉害厉害！！！ 挺好的，分析过程 大佬太牛了，学习了学习了 不明觉厉！！！ 真的是不明觉厉了{:1_921:}