iOS逆向之Frida Hook绕过人脸识别

*本文不涉及任何漏洞，本文仅限技术研究与讨论，严禁用于非法用途，否则产生的一切后果自行承担。

0×00前言

解决问题的手段有很多种，也许存在优劣之分，这次选择了其中一种不那么好玩的方法——frida hook。

人脸识别校验状态存储在服务端，因此即使通过该种方法绕过客户端人脸识别，由于并未获得合法session，所以并无任何实际危害，仅做为IOS Hook学习思路。

0×01准备

越狱IOS(12.4.4)

Frida

lxhToolHTTPDecrypt

app一个

登录时存在人脸识别：

0×02 脱壳&安装

CrackerXI+脱壳，ReProvision签名一条龙，有疑问的可以参考上一篇文章。一毛一样的app。

0×03 寻找关键函数

CrackerXI+脱壳后，二进制文件拉出来拖到ida中分析找到关键函数：

XXXXBaseViewController loginSuccessIsNeedBind:WithInfo:

void __cdecl -[XXXXAPPBaseViewController loginSuccessIsNeedBind:WithInfo:](XXXXAPPBaseViewController *self, SEL a2, bool a3, id a4)
{
  BOOL v4; // w22
  XXXXAPPBaseViewController *v5; // x21
  __int64 v6; // x19
  void *v7; // x0
  void *v8; // x0
  void *v9; // x23
  void *v10; // x0
  void *v11; // x20
  XXXXAPPLoginHelper *v12; // x0
  void *v13; // x23
  __int64 v14; // x1
  __int64 v15; // x1
  __int64 v16; // x0
  struct objc_object *v17; // x0
  void *v18; // x0
  void *v19; // x22
  void *v20; // x0
  void *v21; // x23
  int v22; // w24
  void *v23; // x0
  void *v24; // x0
  __int64 v25; // x22
  void *v26; // x0
  __int64 v27; // x23
  const char *v28; // x1
  void **v29; // [xsp+0h] [xbp-70h]
  __int64 v30; // [xsp+8h] [xbp-68h]
  __int64 (__fastcall *v31)(); // [xsp+10h] [xbp-60h]
  void *v32; // [xsp+18h] [xbp-58h]
  XXXXAPPBaseViewController *v33; // [xsp+20h] [xbp-50h]
  __int64 v34; // [xsp+28h] [xbp-48h]
  __int64 v35; // [xsp+30h] [xbp-40h]
  bool v36; // [xsp+38h] [xbp-38h]
  v4 = a3;//赋值v4
  v5 = self;
  v6 = objc_retain(a4, a2);
  v7 = objc_msgSend(&OBJC_CLASS___UIApplication, "sharedApplication");
  v8 = (void *)objc_retainAutoreleasedReturnValue(v7);
  v9 = v8;
  v10 = objc_msgSend(v8, "delegate");
  v11 = (void *)objc_retainAutoreleasedReturnValue(v10);
  objc_release(v9);
  if ( (unsigned int)-[XXXXAPPBaseViewController needInputIDCardInfomation:](v5, "needInputIDCardInfomation:", v6) )
  {
    +[PCUtil setObject:forKey:](&OBJC_CLASS___PCUtil, "setObject:forKey:", CFSTR("1"), CFSTR("maybeNeedBackLoginGuide"));
    v12 = +[XXXXAPPLoginHelper sharedInstance](&OBJC_CLASS___XXXXAPPLoginHelper, "sharedInstance");
    v13 = (void *)objc_retainAutoreleasedReturnValue(v12);
    v29 = _NSConcreteStackBlock;
    v30 = 3254779904LL;
    v31 = sub_1000B05E4;
    v32 = &unk_10263F2D8;
    v33 = v5;
    v36 = v4;
    v34 = objc_retain(v11, v14);
    v35 = objc_retain(v6, v15);
    objc_msgSend(
      v13,
      "setCompleteGuideBlock:",
      &v29,
      _NSConcreteStackBlock,
      3254779904LL,
      sub_1000B05E4,
      &unk_10263F2D8,
      v5);
    objc_release(v13);
    objc_release(v35);
    v16 = v34;
LABEL_9:
    objc_release(v16);
    goto LABEL_10;
  }
  if ( v4 ) //判断v4(bool)值,确定是否进入人脸识别
  {
    v17 = +[PNCMBankGlobal sharedData](&OBJC_CLASS___PNCMBankGlobal, "sharedData");
    v18 = (void *)objc_retainAutoreleasedReturnValue(v17);
    v19 = v18;
    v20 = objc_msgSend(v18, "bindType");
    v21 = (void *)objc_retainAutoreleasedReturnValue(v20);
    v22 = (unsigned __int64)objc_msgSend(v21, "isEqualToString:", CFSTR("FACE"));
    objc_release(v21);
    objc_release(v19);
    v23 = objc_msgSend(v11, "rootVC");
    v24 = (void *)objc_retainAutoreleasedReturnValue(v23);
    v25 = (__int64)v24;
    v26 = objc_msgSend(v24, "navigationController");
    v27 = objc_retainAutoreleasedReturnValue(v26);
    if ( v22 )
      v28 = "goToFaceCheckBindVC:info:";
    else
      v28 = "goSmsOrUKBindInfoVC:info:";
    objc_msgSend(v5, v28, v27, v6);
    objc_release(v27);
    v16 = v25;
    goto LABEL_9;
  }
  -[XXXXAPPBaseViewController AfterBindSuccess:isNeedBind:](v5, "AfterBindSuccess:isNeedBind:", v6, 0LL);
LABEL_10:
  objc_release(v11);
  objc_release(v6);
}

分析代码发现：

void __cdecl -[XXXXAPPBaseViewController loginSuccessIsNeedBind:WithInfo:](XXXXAPPBaseViewController *self, SEL a2, bool a3, id a4)
v4 = a3;
//...
if ( v4 ) 
{
//...
//人脸识别函数
//...
}

其中a3是参数传入，只要我们hook -[XXXXAPPBaseViewController loginSuccessIsNeedBind:WithInfo:]使其传入bool参数a3为永假，即可不进入人脸识别判断。

手机中启动frida-server（手机中的frida版本须和PC中的版本一致）:

PC上启动lxhToolHTTPDecrypt（ps：不使用该 工具 也可以，使用frida脚本能够直接查找类名函数等，但这个工具图形化界面比较直观，也有一些其他功能）

访问 http://127.0.0.1:8088 选择Identifier

在Hook里选择类名

进入人脸识别时hook到该函数：

0×04 HOOK

编写hook脚本hooking.js：

var search_class = ['XXXXXXBaseViewController'];
var search_method = ['loginSuccessIsNeedBind:WithInfo:'];
function search_methods(className) {
var methods_found = [];
var methods = ObjC.classes[className].$ownMethods;
if (Array.isArray(search_method) && search_method.length) { //search_method not empty
for (var j = 0; j < search_method.length; j++) {
if (methods.join(' ').toLowerCase().includes(search_method[j].toLowerCase())) {
for (var i = 0; i < methods.length; i++){
if (methods[i].toLowerCase().includes(search_method[j].toLowerCase())) {
methods_found.push(methods[i]);
}
}
}
}
}
else {
var methods = ObjC.classes[className].$ownMethods;
for (var i = 0; i < methods.length; i++){
methods_found.push(methods[i]);
}
}
return methods_found;
}
function search_classes(){
var classes_found = [];
for (var className in ObjC.classes) {
if (Array.isArray(search_class) && search_class.length) {
for (var i = 0; i < search_class.length; i++) {
if (className.toLowerCase().includes(search_class[i].toLowerCase())) {
classes_found.push(className);
}
}
}
}
return classes_found;
}
function print_arguments(args) {
var n = 100;
var last_arg = '';
for (var i = 2; i < n; ++i) {
var arg = (new ObjC.Object(args[i])).toString();
if (arg == 'nil' || arg == last_arg) {
break;
}
last_arg = arg;
console.log('\t[-] arg' + i + ': ' + (new ObjC.Object(args[i])).toString());
}
}
if (ObjC.available)
{
console.log('\n[*] Starting Hooking');
var classes_found = search_classes();
for (var i = 0; i < classes_found.length; ++i) {
var methods_found = 0;
methods_found = search_methods(classes_found[i]);
if (Object.keys(methods_found).length){
console.log(classes_found[i]);
}
for (var j = 0; j < methods_found.length; ++j) {
var _className = "" + classes_found[i];
var _methodName = "" + methods_found[j];
var hooking = ObjC.classes[_className][_methodName];
console.log('   ' + methods_found[j]);
Interceptor.attach(hooking.implementation, {
onEnter: function (args) {
this._className = ObjC.Object(args[0]).toString();
this._methodName = ObjC.selectorAsString(args[1]);
console.log('Detected call to:');
console.log('   ' + this._className + ' --> ' + this._methodName);
//print_arguments(args);
},
onLeave: function(returnValues) {
}
});
}
}
console.log('\n[*] Starting Intercepting');
}
else {
console.log('Objective-C Runtime is not available!');
}

执行

frida -l hooking.js -U “appname”

从图上可见hook成功

编写onEnter Hook传入参数修改成0×0：

onEnter: function (args) { 
this._className = ObjC.Object(args[0]).toString();
this._methodName = ObjC.selectorAsString(args[1]);
console.log('Detected call to:');
console.log('   ' + this._className + ' --> ' + this._methodName);
console.log('[-]原始值：'+ args[2]);
args[2]=ptr("0x0");
console.log('[+]修改值：'+ args[2]);
//print_arguments(args);
},

运行Hook:

进入app输入密码登录，已不存在人脸识别。

但登录后由于人脸识别验证在服务端，客户端中并无数据，因此无实际危害。