Janus 二元神漏洞测试

同步发表于：http://blog.hacktons.cn/2017/12/25/janus-demo/

背景

12月9号，Andorid对外曝光了一个名为Janus的重量级系统漏洞CVE-2017-13156), 由安全研究公司Guard Square发现。
Janus原意是神话中的二元身，用于描述这个漏洞还真是贴切。

整个漏洞其实创建在文件校验规则之上：

一个文件便是APK，又是DEX，在安装APK和执行阶段的校验规则差别，致使能够在APK头部附加一个恶意DEX来欺骗系统

下面咱们从市场上随意下载一个apk来作测试。

测试APK

本文涉及的测试APK，只用于单击研究之用，请勿恶意散播或上传，由此引起的纠纷与做者无关

能够从豌豆荚，应用宝等市场下一个测试用的APK,为了方便，咱们须要选用一些体积较小的apk，若是apk较大颇有可能通过了分包，替换工做会麻烦点。

这里比较恶心的是，下载到的apk并非咱们选取的安装包，而是豌豆荚市场，既然豌豆荚这么强势要入镜，那么姑且直接分析豌豆荚市场吧。

MD5 (Wandoujia_224660_web_inner_referral_binded.apk) = d3c1d9b2a74a3f8fd9fce38d38423c58

签名检查

首先检查下豌豆荚的这个apk是否是v2签名的，由于咱们要测试的Janus只能在v1下验证

检查签名信息能够经过*.SF来确认，根据公开信息，若是v2签名的话，会在SF文件内写入一个字段X-Android-APK-Signed:2；
豌豆荚的SF文件名字是META-INF/DEAMON2.SF, 比较幸运啊，能够确认其使用的就是v1签名。

aven$ unzip -l Wandoujia_224660_web_inner_referral_binded.apk |grep META-INF
   120009  12-15-17 14:38   META-INF/MANIFEST.MF
   120130  12-15-17 14:38   META-INF/DEAMON2.SF
      891  12-15-17 14:38   META-INF/DEAMON2.RSA

aven$ unzip -p Wandoujia_224660_web_inner_referral_binded.apk META-INF/DEAMON2.SF|less
Signature-Version: 1.0
SHA1-Digest-Manifest-Main-Attributes: jq/6qzaCk3O+H4OBJsDhMXm+FvE=
Created-By: 1.6.0_30 (Sun Microsystems Inc.)
SHA1-Digest-Manifest: Dts4zfEM9pZstNDahVfVh4e4jGA=

Name: res/drawable-xhdpi-v4/il.png
SHA1-Digest: QCves3Cr/wm3X2w4PR4ESXGMBOw=

Name: res/layout/dh.xml
SHA1-Digest: DCuKb0PRLuNV6jTEbSDGMTEW174=

包名确认

接下来咱们须要构造一个新的dex，嫁接到豌豆荚的apk前面；这里须要确认豌豆荚使用的包名：com.wandoujia.phoenix2

package: name='com.wandoujia.phoenix2' versionCode='16861' versionName='5.68.21'
sdkVersion:'14'
targetSdkVersion:'16'

另外值得一提的是，豌豆荚的权限仍是比较流氓的会要求大量敏感权限，所以在使用该市场的时候注意权限的问题，不然颇有可能裸奔了：

好比读/写短信，读/写通信录等等，还有一些第三方权限

uses-permission:'android.permission.READ_SMS'
uses-permission:'android.permission.RECEIVE_SMS'
uses-permission:'android.permission.MANAGE_ACCOUNTS'
uses-permission:'android.permission.AUTHENTICATE_ACCOUNTS'
uses-permission:'android.permission.USE_CREDENTIALS'
uses-permission:'android.permission.READ_SETTINGS'
uses-permission:'android.permission.READ_EXTERNAL_STORAGE'
uses-permission:'android.permission.SEND_SMS'
uses-permission:'android.permission.WRITE_EXTERNAL_STORAGE'
uses-permission:'android.permission.MOUNT_UNMOUNT_FILESYSTEMS'
uses-permission:'android.permission.INTERNET'
uses-permission:'android.permission.ACCESS_NETWORK_STATE'
uses-permission:'android.permission.ACCESS_WIFI_STATE'
uses-permission:'android.permission.CHANGE_WIFI_STATE'
uses-permission:'android.permission.CHANGE_WIFI_MULTICAST_STATE'
uses-permission:'android.permission.SET_WALLPAPER'
uses-permission:'android.permission.SET_WALLPAPER_HINTS'
uses-permission:'android.permission.WRITE_SETTINGS'
uses-permission:'android.permission.CAMERA'
uses-permission:'android.permission.FLASHLIGHT'
uses-permission:'com.android.launcher.permission.INSTALL_SHORTCUT'
uses-permission:'com.android.launcher.permission.UNINSTALL_SHORTCUT'
uses-permission:'android.permission.READ_PHONE_STATE'
uses-permission:'android.permission.MODIFY_AUDIO_SETTINGS'
uses-permission:'android.permission.SYSTEM_ALERT_WINDOW'
uses-permission:'android.permission.ACCESS_SUPPERUSER'
uses-permission:'android.permission.GET_PACKAGE_SIZE'
uses-permission:'android.permission.KILL_BACKGROUND_PROCESSES'
uses-permission:'android.permission.CLEAR_APP_CACHE'
uses-permission:'android.permission.DISABLE_KEYGUARD'
uses-permission:'com.android.launcher.permission.READ_SETTINGS'
uses-permission:'com.android.launcher.permission.WRITE_SETTINGS'
uses-permission:'com.android.launcher3.permission.READ_SETTINGS'
uses-permission:'com.android.launcher3.permission.WRITE_SETTINGS'
uses-permission:'com.meizu.flyme.launcher.permission.READ_SETTINGS'
uses-permission:'com.meizu.flyme.launcher.permission.WRITE_SETTINGS'
uses-permission:'org.adw.launcher.permission.READ_SETTINGS'
uses-permission:'org.adw.launcher.permission.WRITE_SETTINGS'
uses-permission:'com.qihoo360.launcher.permission.READ_SETTINGS'
uses-permission:'com.qihoo360.launcher.permission.WRITE_SETTINGS'
uses-permission:'com.lge.launcher.permission.READ_SETTINGS'
uses-permission:'com.lge.launcher.permission.WRITE_SETTINGS'
uses-permission:'net.qihoo.launcher.permission.READ_SETTINGS'
uses-permission:'net.qihoo.launcher.permission.WRITE_SETTINGS'
uses-permission:'org.adwfreak.launcher.permission.READ_SETTINGS'
uses-permission:'org.adwfreak.launcher.permission.WRITE_SETTINGS'
uses-permission:'com.huawei.launcher3.permission.READ_SETTINGS'
uses-permission:'com.huawei.launcher3.permission.WRITE_SETTINGS'
uses-permission:'com.fede.launcher.permission.READ_SETTINGS'
uses-permission:'com.fede.launcher.permission.WRITE_SETTINGS'
uses-permission:'com.sec.android.app.twlauncher.settings.READ_SETTINGS'
uses-permission:'com.sec.android.app.twlauncher.settings.WRITE_SETTINGS'
uses-permission:'com.anddoes.launcher.permission.READ_SETTINGS'
uses-permission:'com.anddoes.launcher.permission.WRITE_SETTINGS'
uses-permission:'com.lenovo.launcher.permission.READ_SETTINGS'
uses-permission:'com.lenovo.launcher.permission.WRITE_SETTINGS'
uses-permission:'com.google.android.launcher.permission.READ_SETTINGS'
uses-permission:'com.google.android.launcher.permission.WRITE_SETTINGS'
uses-permission:'com.oppo.launcher.permission.WRITE_SETTINGS'
uses-permission:'com.oppo.launcher.permission.READ_SETTINGS'
uses-permission:'com.yulong.android.launcher3.permission.WRITE_SETTINGS'
uses-permission:'com.yulong.android.launcher3.permission.READ_SETTINGS'
uses-permission:'com.huawei.android.launcher.permission.READ_SETTINGS'
uses-permission:'com.huawei.android.launcher.permission.WRITE_SETTINGS'
uses-permission:'com.htc.launcher.permission.READ_SETTINGS'
uses-permission:'com.htc.launcher.permission.WRITE_SETTINGS'
uses-permission:'com.bbk.launcher2.permission.READ_SETTINGS'
uses-permission:'com.bbk.launcher2.permission.WRITE_SETTINGS'
uses-permission:'android.permission.WAKE_LOCK'
uses-permission:'android.permission.BROADCAST_PACKAGE_ADDED'
uses-permission:'android.permission.BROADCAST_PACKAGE_CHANGED'
uses-permission:'android.permission.BROADCAST_PACKAGE_INSTALL'
uses-permission:'android.permission.BROADCAST_PACKAGE_REPLACED'
uses-permission:'android.permission.RESTART_PACKAGES'
uses-permission:'android.permission.GET_TASKS'
uses-permission:'android.permission.RECEIVE_BOOT_COMPLETED'
uses-permission:'android.permission.CHANGE_NETWORK_STATE'
uses-permission:'android.permission.GET_ACCOUNTS'
uses-permission:'android.permission.VIBRATE'
uses-permission:'android.permission.BIND_ACCESSIBILITY_SERVICE'
uses-permission:'android.permission.READ_CONTACTS'
uses-permission:'android.permission.WRITE_CONTACTS'
uses-permission:'android.permission.CALL_PHONE'
uses-permission:'android.permission.WRITE_SMS'
uses-permission:'android.permission.WRITE_CALL_LOG'
uses-permission:'android.permission.READ_CALL_LOG'
uses-permission:'android.permission.AUTHENTICATE_ACCOUNTS'
uses-permission:'android.permission.WRITE_SYNC_SETTINGS'
uses-permission:'android.permission.MANAGE_ACCOUNTS'
uses-permission:'android.permission.ACCESS_FINE_LOCATION'
uses-permission:'android.permission.ACCESS_COARSE_LOCATION'
uses-permission:'com.wandoujia.phoenix2.permission.MIPUSH_RECEIVE'
uses-permission:'android.permission.PACKAGE_USAGE_STATS'
uses-permission:'android.permission.PERSISTENT_ACTIVITY'
uses-permission:'android.permission.ACCESS_MTK_MMHW'

Hack

接下来开始编码工做，明确下咱们的目标：

• 替换Application，而且在app进程启动时弹出一个toast；
• 替换启动页，显示一个特殊文案；

所以首先安确认下豌豆荚的自定义application：com.pp.assistant.PPApplication。

aven$ aapt dump xmltree Wandoujia_224660_web_inner_referral_binded.apk AndroidManifest.xml|less

    E: application (line=155)
      A: android:theme(0x01010000)=@0x7f0a0001
      A: android:label(0x01010001)=@0x7f0c038a
      A: android:icon(0x01010002)=@0x7f02009d
      A: android:name(0x01010003)="com.pp.assistant.PPApplication" (Raw: "com.pp.assistant.PPApplication")
      A: android:stateNotNeeded(0x01010016)=(type 0x12)0xffffffff
      A: android:windowSoftInputMode(0x0101022b)=(type 0x11)0x3
      A: android:allowBackup(0x01010280)=(type 0x12)0xffffffff

建立同名的PPApplication的，而后加上toast便可，接下来编译获得新的apk，并将其中的dex抽离出来备用。

插曲

在实际插入dex的时候，遇到了一些小插曲，好比插入完后，启动崩溃，因此若是是插入全新的dex的话，须要确认和原有dex的关系，若是彻底摒弃原有逻辑，那么须要手动补全manifest中声明的ContentProvider和BroadcastReceiver，Activity根据须要替换，Service可选替换

另外合并apk和dex不是简单的字节叠加，须要修改最终apk的偏移量，确保zip的正确性。笔者使用的是一个Python脚本

https://github.com/V-E-O/PoC/tree/master/CVE-2017-13156

效果

搞定以后，能够直接安装apk，也能够覆盖升级安装，接下来启动app就能够看到彻底不一样的效果；

在这里咱们出于实验性质，将豌豆荚市场的application和启动Activity作了总体替换，所以直接感觉就是原有逻辑所有没有了，若是咱们经过反编译后增量修改的方式来新增dex，纳闷能够实现和原app功能几乎一致的串改，这样能够恶意插入代码，同时不容易被用户发现。

修复

这个bug看起来挺严重的，不过实际上影响有限，若是用户经过正规市场下载程序基本没什么问题，同时Android官方已经作fix，相信后续很快就会在新版本中生效。 对于开发者来讲比较被动，最好升级签名为V2，别的就没有屏蔽办法了，比较问题出在系统校验上面。