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(); } }
客户端的重要代码在client.newCall()上，上面是okhttp官网的一个示例。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$Factory
其实client.newCall终会通过URL获取一个connection
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
这里的urlConnection其实就是HttpURLConnectionImpl的实例，该类有getInputStream getOutputStream方法，内部分别会调用HttpEngine的getBufferedRequestBody，getResponse。刚开始我尝试hook过这两个接口，比如hook getResponse后，可以将response打印出来.
后来我发现，Request只能输出header，无法输出body。所以又埋头继续分析，getBufferedRequestBody这个函数刚好可以入手，获取一个sink，最后以RetryableSink为突破点，比如hook 其write函数就可以将body打印出来。write函数对应于app层面的urlConnection.getOutputStream().write。
后来发现一个Request,调用getBufferedReuqestBody函数可能不止一次，所以会有数据重复的问题，后来我又寻找到了CacheStrategy$Factory.get点进行Hook，发现还是有数据重复。发现以上hook均有弊端
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数据重复
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非okhttp调用无法抓取
然后还打印了从native层的send,sendmsg,write,recv,read开始的调用栈。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)
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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 -
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.$new(); requestBody.writeTo(BufferObj); Logd(TAG, "nrequest body :n" + BufferObj.readString() + "n"); } }; -
android.os.Bundle打印，需要将Bundle unparcel
var printIntentAndExtras = function printIntentAndExtras(intentObj) { if (intentObj == null) return; var Intent = Java.use("android.content.Intent"); var Bundle = Java.use("android.os.Bundle"); var bundleObj = Intent.getExtras.call(intentObj); if (bundleObj != null) { Bundle.getSize.call(bundleObj, null);//调用getSize即可反序列化 } Logd(TAG, ‘printIntentAndExtras ’ + bundleObj); };
踩到的坑其实不只上面的，刚开始也百度过一些frida网络拦截的方案，还仔细的研究了okhttp的Interceptor方案，最后发现app也是用了拦截器，所以就发生冲突，导致无法使用该方案。
也纯粹的分析过app的smali，寻找调用栈以及网络请求，最后，只有几个比较小的收获，可能对读者没有用处，不过记录一下，方便自己以后回忆。
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java.net.URL拦截
var URLHook = function() { var URL = Java.use('java.net.URL'); URL.openConnection.overload().implementation = function() { var retval = this.openConnection(); Logd('URL', openConnection' + retval); return retval; }; };//URL.openConnection调用概率比较大，但是不一定对网络进行请求 -
拦截app调用http请求前使用json的地方，这只是其中之一
var jsonHook = function() { var xx = Java.use('e.h.a.a');//app smali var xxa_method = xx.a.overload('org.json.JSONObject', 'java.lang.String', 'java.lang.String'); xxa_method.implementation = function(jsonObj, str1, str2) { Logd("json", jsonObj + " str1: " + str1 + " str2" + str2); xxa_method.call(this, jsonObj, str1, str2); } } -
trace http相关class
var traceAllHttpClass = function() { Java.perform(function() { Java.enumerateLoadedClasses({ onMatch: function(name, handle) { /*"e.h.a.a$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() { } }); }); }; -
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; } -
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; } } } });
即使直接强制verify返回true，仍然无法登录，因为出现了相同的ssl问题错误。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><trust-anchors><certificates></certificates><!--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。因此，在周日利用抓包工具和各种从百度上找到的方法，逐步解决遇到的问题。
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"}}
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