一 . 埋头分析踩坑路

从系统的角度去寻找hook点，而不是为了抓包而抓包。

1.okhttp调用流程

public static final MediaType JSON
= MediaType.get("application/json; charset=utf-8");
​
OkHttpClient client = new OkHttpClient();
​
String post(String url, String json) throws IOException {
RequestBody body = RequestBody.create(json, JSON);
Request request = new Request.Builder()
.url(url)
.post(body)
.build();
try (Response response = client.newCall(request).execute()) {
return response.body().string();
}
}

上面是okhttp官网的一个demo，关键代码就在client.newCall。从此处接口调用开始，终会调用至okhttp框架, okhttp本是sdk，后来aosp已经集成至系统，所以可以归类至框架层。

框架层不详述，主要就是这几个java类:

com.android.okhttp.internal.huc.HttpURLConnectionImpl
com.android.okhttp.internal.http.HttpEngine
com.android.okhttp.internal.http.RetryableSink
com.android.okhttp.internal.http.CacheStrategy$Factory

其实client.newCall终会通过URL获取一个connection

HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();

这里的urlConnection其实就是HttpURLConnectionImpl的实例，该类有getInputStream getOutputStream方法，内部分别会调用HttpEngine的getBufferedRequestBody，getResponse。刚开始我尝试hook过这两个接口，比如hook getResponse后，可以将response打印出来.

之后我发现Request只能打印header，并不能打印body。所以又埋头继续分析，getBufferedRequestBody这个函数刚好可以入手，获取一个sink，最后以RetryableSink为突破点，比如hook 其write函数就可以将body打印出来。write函数对应于app层面的urlConnection.getOutputStream().write。

后来发现一个Request,调用getBufferedReuqestBody函数可能不止一次，所以会有数据重复的问题，后来我又寻找到了CacheStrategy$Factory.get点进行Hook，发现还是有数据重复。发现以上hook均有弊端

• 数据重复

• 非okhttp调用无法抓取

接着又继续从native层的send,sendmsg,write,recv,read打印调用栈。最后折腾了三天，决定放弃治疗，还是采取工具吧。

okhttp流程：sdk接口->okhttp框架->native(libc)

2.分析过程中frida踩到的坑(重点都在注释中)

1. android.util.Log不打印

   var Logd = function Logd(tag, msg) {
   Java.use("android.util.Log").d(tag, msg);
   };
   
   
   Logd('http-body-', '11111111111111');//该log不打印
   Logd('http-body', '11111111111111');//该log打印

2. 匿名内部类获取成员需要反射

   var printRequest = function(request) {
   var Buffer = Java.use("com.android.okhttp.okio.Buffer");
   var bodyField = request.getClass().getDeclaredField('body');
   bodyField.setAccessible(true);
   ​
   if (request == null) return;
   Logd('http', 'printRequest: request' + request);
   //var requestBody = request.body();//gadget直接报错
   var requestBody = bodyField.get(request);
   ​
   var requestBodyClass = requestBody.getClass();
   var ClassInstanceArray = Java.array('java.lang.Class', []);
   ​
   //var contentLengthMethod = requestBodyClass.getMethod("contentLength");//gadget直接报错
   var contentLengthMethod = requestBodyClass.getMethod("contentLength", ClassInstanceArray);
   
   contentLengthMethod.setAccessible(true);
   var ObjectInstanceArray = Java.array('java.lang.Object', []);
   var contentLength = requestBody ? contentLengthMethod.invoke(requestBody, ObjectInstanceArray) : 0;
   //if (contentLength == 0) contentLength = contentLen;
   Logd('http', 'printRequest contentLength: ' + contentLength);
   if (contentLength > 0) {
   var BufferObj = Buffer.$new();
   requestBody.writeTo(BufferObj);
   Logd(TAG, "\nrequest body :\n" + BufferObj.readString() + "\n");
   }
   };

3. android.os.Bundle打印，需要将Bundle unparcel

   var printIntentAndExtras = function printIntentAndExtras(intentObj) {
   if (intentObj == null) return;
   var Intent = Java.use("android.content.Intent");
   var Bundle = Java.use("android.os.Bundle");
   var bundleObj = Intent.getExtras.call(intentObj);
   
   if (bundleObj != null) {
   Bundle.getSize.call(bundleObj, null);//调用getSize即可反序列化
   }
   
   Logd(TAG, ‘printIntentAndExtras ’ + bundleObj);
   };

踩到的坑其实不只上面的，刚开始也百度过一些frida网络拦截的方案，还仔细的研究了okhttp的Interceptor方案，最后发现app也是用了拦截器，所以就发生冲突，导致无法使用该方案。

也纯粹的分析过app的smali，寻找调用栈以及网络请求，最后，只有几个比较小的收获，可能对读者没有用处，不过记录一下，方便自己以后回忆。

1. java.net.URL拦截

   var URLHook = function() {
   var URL = Java.use('java.net.URL');
   URL.openConnection.overload().implementation = function() {
   var retval = this.openConnection();
   Logd('URL', openConnection' + retval);
   return retval;
   };
   };//URL.openConnection调用概率比较大，但是不一定对网络进行请求

2. 拦截app调用http请求前使用json的地方，这只是其中之一

   var jsonHook = function() {
   var xx = Java.use('e.h.a.a');//app smali
   var xxa_method = xx.a.overload('org.json.JSONObject', 'java.lang.String', 'java.lang.String');
   xxa_method.implementation = function(jsonObj, str1, str2) {
   Logd("json", jsonObj + " str1: " + str1 + " str2" + str2);
   xxa_method.call(this, jsonObj, str1, str2);
   }
   }

3. trace http相关class

   var traceAllHttpClass = function() {
   Java.perform(function() {
   Java.enumerateLoadedClasses({
   onMatch: function(name, handle) {
   /*"e.h.a.a$a",起初也拦截过app的该混淆类*/
   if (name.indexOf("com.android.okhttp.Http") != -1 || name.indexOf("com.android.okhttp.Request") != -1
   || name.indexOf("com.android.okhttp.internal") != -1) {
   traceClass(name);//对这三个class进行trace
   }
   },
   onComplete: function() {
   }
   });
   });
   };

4. Request$Builder拦截

   var BuilderClass = Java.use('com.android.okhttp.Request$Builder')
   ​
   BuilderClass.build.implementation = function () {
   //LOG('com.android.okhttp.HttpUrl$Builder.build overload', { c: Color.Light.Cyan });
   //printBacktrace();
   var retval = this.build();
   Logd(TAG, "retval:" + retval);
   printRequest(retval);
   return retval;
   }

5. property_get拦截

   var nativePropertyGetAddr = Module.findExportByName(null, '__system_property_get');
   Interceptor.attach(nativePropertyGetAddr, {
   onEnter: function onEnter(args) {
   this._name = args[0].readCString();
   this._value = args[1];
   },
   onLeave: function onLeave(retval) {
   if (this._name.indexOf("ro.build.id") != -1) {
   var virtualDevice = getVirtualDevice();
   if (DEBUG_PROP) Logd(TAG, "__system_property_get fake " + this._name + "=>to " + virtualDevice.build_id);
   
   this._value.writeUtf8String(virtualDevice.build_id);
   }
   
   var strFilter = /^ro\./g;
   if (DEBUG_PROP && this._name.match(strFilter) != null) Logd(TAG, "__system_property_get " + this._name);
   }
   });

二 . 设备android_id导致用户过期的处理

var DEBUG_PROP = false;
var DEVICE_CONFIG = "/sdcard/.device";
​
function getVirtualDevice() {
var nativeOpen = new NativeFunction(Module.findExportByName(‘libc.so’, 'open'), 'int', ['pointer', 'int']);
var nativeRead = new NativeFunction(Module.findExportByName('libc.so', 'read'), 'int', ['int', 'pointer', 'int']);
var fd = nativeOpen(Memory.allocUtf8String(DEVICE_CONFIG), 0);
var mem = Memory.alloc(1024);
var readLen = nativeRead(fd, mem, 1024);
var json = JSON.parse(mem.readCString(readLen));
return json;
}
​
Secure.getString.implementation = function () {
var retval = this.getString(arguments[0], arguments[1]);
if (DEBUG_PROP) Logd(TAG, "Settings.Secure get " + arguments[1] + " val " + retval);

if (arguments[1].indexOf("android_id") != -1) {
var virtualDevice = getVirtualDevice();
return virtualDevice.android_id;
}

return retval;
};

三 . 使用抓包工具fiddle抓包脱坑

1.fiddle代理设置OK，app却无法登陆

分析adb log,进程有 java.security.cert.CertPathValidatorException的打印，之前也看过一些frida拦截抓包绕过证书的帖子。先试一把暴力搜索：

Java.perform(function(){
const groups = Java.enumerateMethods('*!verify/u');
var classes = null;
for(var i in groups){
var classes = groups[i]['classes'];

for(var i in classes){
Java.use(classes[i]['name'])
.verify
.overload('java.lang.String', 'javax.net.ssl.SSLSession')
.implementation = function() {
printBacktrace();
LOG("[+] invoke verify", { c: Color.Red });
return true;
}
}
}
});

调用verify直接暴力返回true，依然无法登陆，报错是同样的ssl问题。百度搜索后找到了答案。apktool解包，然后修改

res/xml/network_security_config.xml
<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
<base-config cleartextTrafficPermitted="true">
<trust-anchors>
<certificates src="system" />
<!--添加fiddle证书可信任
<certificates src="user" />
-->
</trust-anchors>
</base-config>
</network-security-config>

重打包签名后运行一把，fiddle抓到了包，app也能正常登陆了，这次也是运气好吧，app的ssl校验只有单向app校验，服务器并没有进行校验。

四.结束

从周二下午一直折腾到周五，最后从系统层面的HttpEngine寻找hook点并不是很好的方法，弊端也已明了。所以趁着周日的时间，再试一下各种百度到的方法----抓包工具，然后一步步将遇到的问题pass掉。

下面是抓到的两个包：

HTTP/1.1 200 OK
Date: Sun, 16 Aug 2020 06:27:34 GMT
Content-Type: application/json
Content-Length: 101
Connection: keep-alive
Grpc-Metadata-Content-Type: application/grpc
Vary: Origin
Vary: Accept-Encoding
​
{"result":{"errno":"OK","errmsg":"成功"},"data":{"version":"xxxxxxxx-351e-40cf-aaa9-3177d6df9b7f"}}
-----------------------------------
HTTP/1.1 200 OK
Date: Sun, 16 Aug 2020 06:27:34 GMT
Content-Type: application/json
Content-Length: 99
Connection: keep-alive
Grpc-Metadata-Content-Type: application/grpc
Vary: Origin
Vary: Accept-Encoding
​
{"result":{"errno":"OK","errmsg":"成功"},"data":{"nodeToken":"xxxxxxxc24d79f55c0b07beaf50cb566"}}

POST https://tap-xxxxxxx.xxxxxx.com/api/v2/Android/analytics/basic HTTP/1.1
Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cjbcjdsabcjvbXVCJ9.eyJ1aWQiOjE4ODMzMDEsInNlY3JldCI6IjAzNzE0M2Y3LTExMTUtNGY2Yi1iNzQxLWUyMjc5ZDM3MGY3MCIsImV4cCI6MTU5NzgxNjQ0MiwiaXNzIjoiZ3Vlc3QgbG9naW4ifQ.W3SiO0-afbhxPITjRinnhyWhZLy1bzZhYexm5VCWklI
X-Device-ID: 9xxxxxxx84d4542e
X-Loc: ["China","Shanghai","Shanghai","","ChinaUnicom","31.224349","121.4767528","Asia/Shanghai","UTC+8","310000","86","CN","AP","xxx.166.xxx.xxx"]
X-App-Version: 2.2.0
Content-Type: application/json; charset=utf-8
Content-Length: 208
Host: xx-xxxx.xxxxxx.com
Connection: Keep-Alive
Accept-Encoding: gzip
User-Agent: okhttp/4.7.2
​
{"deviceID":"9xxxxxxx84d4542e","model":"V1813BA","systemVersion":"9","version":"2.2.0","location":{"latitude":xx.x99x990990991,"longitude":xxx.26689769073256},"network":{"g2":0,"g3":0,"g4":4,"g5":0,"wifi":4}}
​
-----------------------------------
HTTP/1.1 200 OK
Date: Sun, 16 Aug 2020 06:27:35 GMT
Content-Type: application/json
Content-Length: 43
Connection: keep-alive
Grpc-Metadata-Content-Type: application/grpc
Vary: Origin
Vary: Accept-Encoding
​
{"result":{"errno":"OK","errmsg":"成功"}}