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解决APP抓包问题【网络安全】

1.前言

在日常渗透过程中我们经常会遇到瓶颈无处下手,这个时候如果攻击者从APP进行突破,往往会有很多惊喜。但是目前市场上的APP都会为防止别人恶意盗取和恶意篡改进行一些保护措施,比如模拟器检测、root检测、APK加固、代码混淆、代码反调试、反脱壳、签名校验等等对抗机制。

而测试人员对APP进行渗透的首步操作通常就是上burp或者Charles这类抓包工具进行抓包,查看请求记录里的域名及链接地址是否可以进一步利用,但是如果遇到一些APP出现证书报错或者抓不到包的情况该怎么办,读过本篇文章之后,相信你会拥有一些新的解决方案和思考。

2.数字证书

我们都知道http协议传输的是明文信息,是可以直接捕获的,从而造成了数据泄露。为了防止中间人的拦截,出现了HTTPS加密机制。在HTTPS中,使用了证书+数字签名解决了这个问题。

此篇的重点在于如何应对APP的抓包对抗。

总结的HTTPS加密机制如下:

  • 数字签名是发送方的明文经历了两次加密得到的两个东西组成,一个是hash ,一个是经过私钥加密。
  • 数字证书就是明文+数字签名。但是数字证书中的内容远不止这俩,还包括了权威机构的信息,服务器的域名,最重要的是有签名的计算方法,不然用公钥进行解密之后的hash,如何与加密明文进行对比呢,还有证书中还包括公钥,公钥用于发放给请求证书的客户端。
  • HTTPS就是使用SSL/TLS协议进行加密传输,让客户端拿到服务器的公钥,然后客户端随机生成一个对称加密的秘钥,使用公钥加密,传输给服务端,后续的所有信息都通过该对称秘钥进行加密解密,完成整个HTTPS的流程。

3.https抓包

导入用户证书

在第一次使用burp时,都会有这么一步,将burp的证书导出,添加进浏览器 【受信任的根证书颁发机构】中去,这样就会信任burp发来的请求包,也就可以请求数据进行修改。我们对APP抓包,也同样要将burp证书安装到系统证书中去,一般从【SD卡安装】的证书会存放在用户信任的凭据下
1666596096_63563d00a4536c6e85054.jpg

image.png

下图是我将burp证书安装到Android7.1.2的用户证书下,使用okhttp对https://ttt.com进行请求的结果。由于ttt.com的SSL证书是自签名证书,而自签名证书是不被系统默认信任的,所以需要先将ttt.com的自签名证书添加到系统证书中才可以访问。
image.png

自签名证书的生成如下图所示:
image.png

  • 系统证书路径:/system/etc/security/cacerts/
  • 用户证书路径:/data/misc/user/0/cacerts-added/

移动到系统根证书路径的方法:

1、导出burp.der

2、使用openssl更改证书格式,先将burp证书的der格式转成pem,再获取证书的hash

openssl x509 -inform DER -in burp.der -out burp.pem
openssl x509 -inform PEM -subject_hash_old -in burp.pem 

image.png

3.移动到系统根证书目录路径下

Android根证书目录都是以pem证书的hash值+.0格式,所以要将刚才生成的pem改名为xxxx.0

mv burp.pem a5ba575.0

由于系统读写权限问题,不一定能直接上传到system目录

adb push 9a5ba575.0 /sdcard

adb shell 
mount -o remount,rw /system
cp /sdcard/9a5ba575.0 /system/etc/security/cacerts/
chmod 644 /system/etc/security/cacerts/9a5ba575.0

移动完成之后,再打开【设置】-【安全】-【信任的凭据】验证一下
image.png

这时可以在Android7.0以上版本正常访问https://ttt.com了,其他抓包工具同理即可。

证书有效期过长

还有一种情况是,导入到系统证书仍抓不到包,并且浏览器会报NET::ERR_CERT_VALIDITY_TOO_LONG错误。

原因是chrome从2018年开始只信任有效期少于825天(27个月)的证书,而burp证书有效期过长。

解决方案是自己做一个低于27个月的root证书导入burp,再通过burp重新导出证书并放入到系统证书路径下。

openssl genrsa -out key.pem 3072 -nodes
openssl req -new -x509 -key key.pem -sha256 -config openssl.cnf -out cert.pem -days 730 -subj "/C=JP/ST=/L=/O=m4bln/CN=MY CA"
openssl pkcs12 -export -inkey key.pem -in cert.pem -out cert_and_key.pfx
把cert_and_key.pfx导入burp

目前还没遇到过这种情况,但是如果遇到了这种问题要知道怎么解决。

4.SSLPinning

对于像ttt.com这种自签名的免费证书,不需要CA权威认证的证书,大多数APP开发商都会使用。那么如果在安卓开发的过程中,将证书的验证逻辑放在APP内部,与系统和浏览器毫无相关,这时再想将burp证书导入系统受信任路径下也于事无补了。

APP自己校验证书,分为两种,一种是将验证逻辑也在代码中,一种是写在安卓7.0之后才有的network-security-config中。

验证是方式也有两种,一种是验证证书公钥的hash值,一种是直接验证证书的公钥文件。

这种通过APP自身的验证方式就叫做证书绑定(也叫Certificate PinningSSL Pinning)。

那么如何去判断一个APP是否使用了证书绑定呢?首先拿到apk文件,用apktool工具进行反编译,查看敏感文件

apktool d -s <file.apk> -o <outdir>

开发人员经常会将网络配置的相关文件保存到指定位置,如下图就指定在了xml目录下。
image.png

所以在反编译后的res/xml目录下会有一个network_security_config.xml文件,打开看到标签,说明使用了证书绑定机制。

image.png

在配置文件中检验的两种方法

<network-security-config xmlns:tools="http://schemas.android.com/tools">
    <!--允许http访问-->
    <base-config cleartextTrafficPermitted="true"
        tools:ignore="InsecureBaseConfiguration" />

    <!--证书校验-->
    <domain-config>
        <domain includeSubdomains="true">www.ttt.com</domain>
        <trust-anchors>
            <certificates src="@raw/ttt"/>
        </trust-anchors>
    </domain-config>

    <!--公钥校验-->
    <domain-config cleartextTrafficPermitted="true">
        <domain includeSubdomains="true">ttt.com</domain>
        <!--利用xml校验证书公钥的hash值-->
        <pin-set expiration="2099-01-01"
            tools:ignore="MissingBackupPin">
            <pin digest="SHA-256">7VMdvZE3PGbxb0Pgf1PlCp+MI8KZ2ZC5psM8TIylNDA=</pin>
        </pin-set>
        <!--利用xml校验证书的公钥文件-->
        <trust-anchors>
            <certificates src="@raw/ttt"/>
        </trust-anchors>
    </domain-config>

</network-security-config>

这两种校验机制出现一种即可,从代码中可以看出,ttt.com就是安卓自己要校验绑定的域名。

如果只是在这个文件进行校验,有两种解决方案:一是直接将文件中校验的部分或注释掉,再重新打包和签名即可,但是这过程又有些麻烦,并不是上上策,如果遇到了不能重打包的apk就尴尬了。。。二是最常用的也是最好用的frida来hook关键函数进行绕过,后面会讲解。当然有些人会直接在真机或者模拟器上安装xposed模块,但是我个人觉得每次使用都要软重启,可能还会造成卡机,所以感觉还是使用frida最方便。

在代码中检验的两种方法

1.利用代码校验证书的公钥hash

String hostname = "www.ttt.com";
CertificatePinner certificatePinner = new CertificatePinner.Builder()
    .add(hostname, "sha256/7VMdvZE3PGbxb0Pgf1PlCp+MI8KZ2ZC5psM8TIylNDA=")
    .build();
OkHttpClient client = new OkHttpClient.Builder()
    .certificatePinner(certificatePinner)
    .hostnameVerifier(new HostnameVerifier() {
        @Override
        public boolean verify(String hostname, SSLSession session) {
            return true;
        }
    }).build();

2.利用代码校验证书的公钥证书文件

// 获取证书输入流
InputStream openRawResource = getApplicationContext().getResources().openRawResource(R.raw.ttt); 
Certificate ca = CertificateFactory.getInstance("X.509").generateCertificate(openRawResource);
// 创建 Keystore 包含我们的证书
KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
keyStore.load(null, null);
keyStore.setCertificateEntry("ca", ca);
// 创建一个 TrustManager 仅把 Keystore 中的证书 作为信任的锚点
TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm()); // 建议不要使用自己实现的X509TrustManager,而是使用默认的X509TrustManager
trustManagerFactory.init(keyStore);
// 用 TrustManager 初始化一个 SSLContext
sslContext = SSLContext.getInstance("TLS");  //定义:public static SSLContext sslContext = null;
sslContext.init(null, trustManagerFactory.getTrustManagers(), new SecureRandom());

OkHttpClient client = new OkHttpClient.Builder()
    .sslSocketFactory(sslContext.getSocketFactory(),
                      (X509TrustManager) trustManagerFactory.getTrustManagers()[0] )
    .hostnameVerifier(new HostnameVerifier() {
        @Override
        public boolean verify(String hostname, SSLSession session) {
            return true;
        }
    }).build();

通过frida进行hook,这种绕过的脚本也很多,比较熟悉的有JustTrustMe和DroidSSLUnpinning,他们的底层原理都是一样的,通过hook关键的验证函数,进行逻辑绕过。

frida的安装过程就不详细讲解了,网上很多教程。这里我使用的是frida 12.8.0 + frida-tools=5.3.0

这里我使用的hook.js的脚本如下:

/*  Android ssl certificate pinning bypass script for various methods
by Maurizio Siddu modify by Ch3nYe

Run with:
frida -U -f [APP_ID] -l frida_multiple_unpinning.js --no-pause
*/
setTimeout(function() {
Java.perform(function () {
console.log('');
console.log('======');
console.log('[#] Android Bypass for various Certificate Pinning methods [#]');
console.log('======');

var X509TrustManager = Java.use('javax.net.ssl.X509TrustManager');
var SSLContext = Java.use('javax.net.ssl.SSLContext');

// TrustManager (Android < 7) //

var TrustManager = Java.registerClass({
// Implement a custom TrustManager
name: 'dev.asd.test.TrustManager',
implements: [X509TrustManager],
methods: {
checkClientTrusted: function (chain, authType) {},
checkServerTrusted: function (chain, authType) {},
getAcceptedIssuers: function () {return []; }
}
});
// Prepare the TrustManager array to pass to SSLContext.init()
var TrustManagers = [TrustManager.$new()];
// Get a handle on the init() on the SSLContext class
var SSLContext_init = SSLContext.init.overload(
'[Ljavax.net.ssl.KeyManager;', '[Ljavax.net.ssl.TrustManager;', 'java.security.SecureRandom');
try {
// Override the init method, specifying the custom TrustManager
SSLContext_init.implementation = function(keyManager, trustManager, secureRandom) {
console.log('[+] Bypassing Trustmanager (Android < 7) request');
SSLContext_init.call(this, keyManager, TrustManagers, secureRandom);
};
} catch (err) {
console.log('[-] TrustManager (Android < 7) pinner not found');
//console.log(err);
}

// OkHTTPv3 (quadruple bypass) //
/
try {
// Bypass OkHTTPv3 {1}
var okhttp3_Activity_1 = Java.use('okhttp3.CertificatePinner');
okhttp3_Activity_1.check.overload('java.lang.String', 'java.util.List').implementation = function (a, b) {
console.log('[+] Bypassing OkHTTPv3 {1}: ' + a);
return true;
};
} catch (err) {
console.log('[-] OkHTTPv3 {1} pinner not found');
//console.log(err);
}
try {
// Bypass OkHTTPv3 {2}
// This method of CertificatePinner.check could be found in some old Android app
var okhttp3_Activity_2 = Java.use('okhttp3.CertificatePinner');
okhttp3_Activity_2.check.overload('java.lang.String', 'java.security.cert.Certificate').implementation = function (a, b) {
console.log('[+] Bypassing OkHTTPv3 {2}: ' + a);
return true;
};
} catch (err) {
console.log('[-] OkHTTPv3 {2} pinner not found');
//console.log(err);
}
try {
// Bypass OkHTTPv3 {3}
var okhttp3_Activity_3 = Java.use('okhttp3.CertificatePinner');
okhttp3_Activity_3.check.overload('java.lang.String', '[Ljava.security.cert.Certificate;').implementation = function (a, b) {
console.log('[+] Bypassing OkHTTPv3 {3}: ' + a);
return true;
};
} catch(err) {
console.log('[-] OkHTTPv3 {3} pinner not found');
//console.log(err);
}
try {
// Bypass OkHTTPv3 {4}
var okhttp3_Activity_4 = Java.use('okhttp3.CertificatePinner');
okhttp3_Activity_4[''].implementation = function (a, b) {
console.log('[+] Bypassing OkHTTPv3 {4}: ' + a);
};
} catch(err) {
console.log('[-] OkHTTPv3 {4} pinner not found');
//console.log(err);
}

// Trustkit (triple bypass) //
//
try {
// Bypass Trustkit {1}
var trustkit_Activity_1 = Java.use('com.datatheorem.android.trustkit.pinning.OkHostnameVerifier');
trustkit_Activity_1.verify.overload('java.lang.String', 'javax.net.ssl.SSLSession').implementation = function (a, b) {
console.log('[+] Bypassing Trustkit {1}: ' + a);
return true;
};
} catch (err) {
console.log('[-] Trustkit {1} pinner not found');
//console.log(err);
}
try {
// Bypass Trustkit {2}
var trustkit_Activity_2 = Java.use('com.datatheorem.android.trustkit.pinning.OkHostnameVerifier');
trustkit_Activity_2.verify.overload('java.lang.String', 'java.security.cert.X509Certificate').implementation = function (a, b) {
console.log('[+] Bypassing Trustkit {2}: ' + a);
return true;
};
} catch (err) {
console.log('[-] Trustkit {2} pinner not found');
//console.log(err);
}
try {
// Bypass Trustkit {3}
var trustkit_PinningTrustManager = Java.use('com.datatheorem.android.trustkit.pinning.PinningTrustManager');
trustkit_PinningTrustManager.checkServerTrusted.implementation = function () {
console.log('[+] Bypassing Trustkit {3}');
};
} catch (err) {
console.log('[-] Trustkit {3} pinner not found');
//console.log(err);
}

// TrustManagerImpl (Android > 7) //

try {
var TrustManagerImpl = Java.use('com.android.org.conscrypt.TrustManagerImpl');
TrustManagerImpl.verifyChain.implementation = function (untrustedChain, trustAnchorChain, host, clientAuth, ocspData, tlsSctData) {
console.log('[+] Bypassing TrustManagerImpl (Android > 7): ' + host);
return untrustedChain;
};
} catch (err) {
console.log('[-] TrustManagerImpl (Android > 7) pinner not found');
//console.log(err);
}

// Appcelerator Titanium //
///
try {
var appcelerator_PinningTrustManager = Java.use('appcelerator.https.PinningTrustManager');
appcelerator_PinningTrustManager.checkServerTrusted.implementation = function () {
console.log('[+] Bypassing Appcelerator PinningTrustManager');
};
} catch (err) {
console.log('[-] Appcelerator PinningTrustManager pinner not found');
//console.log(err);
}

// OpenSSLSocketImpl Conscrypt //
/
try {
var OpenSSLSocketImpl = Java.use('com.android.org.conscrypt.OpenSSLSocketImpl');
OpenSSLSocketImpl.verifyCertificateChain.implementation = function (certRefs, JavaObject, authMethod) {
console.log('[+] Bypassing OpenSSLSocketImpl Conscrypt');
};
} catch (err) {
console.log('[-] OpenSSLSocketImpl Conscrypt pinner not found');
//console.log(err);
}

// OpenSSLEngineSocketImpl Conscrypt //
///
try {
var OpenSSLEngineSocketImpl_Activity = Java.use('com.android.org.conscrypt.OpenSSLEngineSocketImpl');
OpenSSLSocketImpl_Activity.verifyCertificateChain.overload('[Ljava.lang.Long;', 'java.lang.String').implementation = function (a, b) {
console.log('[+] Bypassing OpenSSLEngineSocketImpl Conscrypt: ' + b);
};
} catch (err) {
console.log('[-] OpenSSLEngineSocketImpl Conscrypt pinner not found');
//console.log(err);
}

// OpenSSLSocketImpl Apache Harmony //
//
try {
var OpenSSLSocketImpl_Harmony = Java.use('org.apache.harmony.xnet.provider.jsse.OpenSSLSocketImpl');
OpenSSLSocketImpl_Harmony.verifyCertificateChain.implementation = function (asn1DerEncodedCertificateChain, authMethod) {
console.log('[+] Bypassing OpenSSLSocketImpl Apache Harmony');
};
} catch (err) {
console.log('[-] OpenSSLSocketImpl Apache Harmony pinner not found');
//console.log(err);
}

// PhoneGap sslCertificateChecker (https://github.com/EddyVerbruggen/SSLCertificateChecker-PhoneGap-Plugin) //
//
try {
var phonegap_Activity = Java.use('nl.xservices.plugins.sslCertificateChecker');
phonegap_Activity.execute.overload('java.lang.String', 'org.json.JSONArray', 'org.apache.cordova.CallbackContext').implementation = function (a, b, c) {
console.log('[+] Bypassing PhoneGap sslCertificateChecker: ' + a);
return true;
};
} catch (err) {
console.log('[-] PhoneGap sslCertificateChecker pinner not found');
//console.log(err);
}

// IBM MobileFirst pinTrustedCertificatePublicKey (double bypass) //

try {
// Bypass IBM MobileFirst {1}
var WLClient_Activity_1 = Java.use('com.worklight.wlclient.api.WLClient');
WLClient_Activity_1.getInstance().pinTrustedCertificatePublicKey.overload('java.lang.String').implementation = function (cert) {
console.log('[+] Bypassing IBM MobileFirst pinTrustedCertificatePublicKey {1}: ' + cert);
return;
};
} catch (err) {
console.log('[-] IBM MobileFirst pinTrustedCertificatePublicKey {1} pinner not found');
//console.log(err);
}
try {
// Bypass IBM MobileFirst {2}
var WLClient_Activity_2 = Java.use('com.worklight.wlclient.api.WLClient');
WLClient_Activity_2.getInstance().pinTrustedCertificatePublicKey.overload('[Ljava.lang.String;').implementation = function (cert) {
console.log('[+] Bypassing IBM MobileFirst pinTrustedCertificatePublicKey {2}: ' + cert);
return;
};
} catch (err) {
console.log('[-] IBM MobileFirst pinTrustedCertificatePublicKey {2} pinner not found');
//console.log(err);
}

// IBM WorkLight (ancestor of MobileFirst) HostNameVerifierWithCertificatePinning (quadruple bypass) //
///
try {
// Bypass IBM WorkLight {1}
var worklight_Activity_1 = Java.use('com.worklight.wlclient.certificatepinning.HostNameVerifierWithCertificatePinning');
worklight_Activity_1.verify.overload('java.lang.String', 'javax.net.ssl.SSLSocket').implementation = function (a, b) {
console.log('[+] Bypassing IBM WorkLight HostNameVerifierWithCertificatePinning {1}: ' + a);
return;
};
} catch (err) {
console.log('[-] IBM WorkLight HostNameVerifierWithCertificatePinning {1} pinner not found');
//console.log(err);
}
try {
// Bypass IBM WorkLight {2}
var worklight_Activity_2 = Java.use('com.worklight.wlclient.certificatepinning.HostNameVerifierWithCertificatePinning');
worklight_Activity_2.verify.overload('java.lang.String', 'java.security.cert.X509Certificate').implementation = function (a, b) {
console.log('[+] Bypassing IBM WorkLight HostNameVerifierWithCertificatePinning {2}: ' + a);
return;
};
} catch (err) {
console.log('[-] IBM WorkLight HostNameVerifierWithCertificatePinning {2} pinner not found');
//console.log(err);
}
try {
// Bypass IBM WorkLight {3}
var worklight_Activity_3 = Java.use('com.worklight.wlclient.certificatepinning.HostNameVerifierWithCertificatePinning');
worklight_Activity_3.verify.overload('java.lang.String', '[Ljava.lang.String;', '[Ljava.lang.String;').implementation = function (a, b) {
console.log('[+] Bypassing IBM WorkLight HostNameVerifierWithCertificatePinning {3}: ' + a);
return;
};
} catch (err) {
console.log('[-] IBM WorkLight HostNameVerifierWithCertificatePinning {3} pinner not found');
//console.log(err);
}
try {
// Bypass IBM WorkLight {4}
var worklight_Activity_4 = Java.use('com.worklight.wlclient.certificatepinning.HostNameVerifierWithCertificatePinning');
worklight_Activity_4.verify.overload('java.lang.String', 'javax.net.ssl.SSLSession').implementation = function (a, b) {
console.log('[+] Bypassing IBM WorkLight HostNameVerifierWithCertificatePinning {4}: ' + a);
return true;
};
} catch (err) {
console.log('[-] IBM WorkLight HostNameVerifierWithCertificatePinning {4} pinner not found');
//console.log(err);
}

// Conscrypt CertPinManager //
//
try {
var conscrypt_CertPinManager_Activity = Java.use('com.android.org.conscrypt.CertPinManager');
conscrypt_CertPinManager_Activity.isChainValid.overload('java.lang.String', 'java.util.List').implementation = function (a, b) {
console.log('[+] Bypassing Conscrypt CertPinManager: ' + a);
return true;
};
} catch (err) {
console.log('[-] Conscrypt CertPinManager pinner not found');
//console.log(err);
}

// CWAC-Netsecurity (unofficial back-port pinner for Android<4.2) CertPinManager //
///
try {
var cwac_CertPinManager_Activity = Java.use('com.commonsware.cwac.netsecurity.conscrypt.CertPinManager');
cwac_CertPinManager_Activity.isChainValid.overload('java.lang.String', 'java.util.List').implementation = function (a, b) {
console.log('[+] Bypassing CWAC-Netsecurity CertPinManager: ' + a);
return true;
};
} catch (err) {
console.log('[-] CWAC-Netsecurity CertPinManager pinner not found');
//console.log(err);
}

// Worklight Androidgap WLCertificatePinningPlugin //
/
try {
var androidgap_WLCertificatePinningPlugin_Activity = Java.use('com.worklight.androidgap.plugin.WLCertificatePinningPlugin');
androidgap_WLCertificatePinningPlugin_Activity.execute.overload('java.lang.String', 'org.json.JSONArray', 'org.apache.cordova.CallbackContext').implementation = function (a, b, c) {
console.log('[+] Bypassing Worklight Androidgap WLCertificatePinningPlugin: ' + a);
return true;
};
} catch (err) {
console.log('[-] Worklight Androidgap WLCertificatePinningPlugin pinner not found');
//console.log(err);
}

// Netty FingerprintTrustManagerFactory //
//
try {
var netty_FingerprintTrustManagerFactory = Java.use('io.netty.handler.ssl.util.FingerprintTrustManagerFactory');
//NOTE: sometimes this below implementation could be useful
//var netty_FingerprintTrustManagerFactory = Java.use('org.jboss.netty.handler.ssl.util.FingerprintTrustManagerFactory');
netty_FingerprintTrustManagerFactory.checkTrusted.implementation = function (type, chain) {
console.log('[+] Bypassing Netty FingerprintTrustManagerFactory');
};
} catch (err) {
console.log('[-] Netty FingerprintTrustManagerFactory pinner not found');
//console.log(err);
}

// Squareup CertificatePinner [OkHTTP<v3] (double bypass) //

try {
// Bypass Squareup CertificatePinner  {1}
var Squareup_CertificatePinner_Activity_1 = Java.use('com.squareup.okhttp.CertificatePinner');
Squareup_CertificatePinner_Activity_1.check.overload('java.lang.String', 'java.security.cert.Certificate').implementation = function (a, b) {
console.log('[+] Bypassing Squareup CertificatePinner {1}: ' + a);
return;
};
} catch (err) {
console.log('[-] Squareup CertificatePinner {1} pinner not found');
//console.log(err);
}
try {
// Bypass Squareup CertificatePinner {2}
var Squareup_CertificatePinner_Activity_2 = Java.use('com.squareup.okhttp.CertificatePinner');
Squareup_CertificatePinner_Activity_2.check.overload('java.lang.String', 'java.util.List').implementation = function (a, b) {
console.log('[+] Bypassing Squareup CertificatePinner {2}: ' + a);
return;
};
} catch (err) {
console.log('[-] Squareup CertificatePinner {2} pinner not found');
//console.log(err);
}

// Squareup OkHostnameVerifier [OkHTTP v3] (double bypass) //
/
try {
// Bypass Squareup OkHostnameVerifier {1}
var Squareup_OkHostnameVerifier_Activity_1 = Java.use('com.squareup.okhttp.internal.tls.OkHostnameVerifier');
Squareup_OkHostnameVerifier_Activity_1.verify.overload('java.lang.String', 'java.security.cert.X509Certificate').implementation = function (a, b) {
console.log('[+] Bypassing Squareup OkHostnameVerifier {1}: ' + a);
return true;
};
} catch (err) {
console.log('[-] Squareup OkHostnameVerifier pinner not found');
//console.log(err);
}
try {
// Bypass Squareup OkHostnameVerifier {2}
var Squareup_OkHostnameVerifier_Activity_2 = Java.use('com.squareup.okhttp.internal.tls.OkHostnameVerifier');
Squareup_OkHostnameVerifier_Activity_2.verify.overload('java.lang.String', 'javax.net.ssl.SSLSession').implementation = function (a, b) {
console.log('[+] Bypassing Squareup OkHostnameVerifier {2}: ' + a);
return true;
};
} catch (err) {
console.log('[-] Squareup OkHostnameVerifier pinner not found');
//console.log(err);
}

// Android WebViewClient (double bypass) //
///
try {
// Bypass WebViewClient {1} (deprecated from Android 6)
var AndroidWebViewClient_Activity_1 = Java.use('android.webkit.WebViewClient');
AndroidWebViewClient_Activity_1.onReceivedSslError.overload('android.webkit.WebView', 'android.webkit.SslErrorHandler', 'android.net.http.SslError').implementation = function (obj1, obj2, obj3) {
console.log('[+] Bypassing Android WebViewClient {1}');
};
} catch (err) {
console.log('[-] Android WebViewClient {1} pinner not found');
//console.log(err)
}
try {
// Bypass WebViewClient {2}
var AndroidWebViewClient_Activity_2 = Java.use('android.webkit.WebViewClient');
AndroidWebViewClient_Activity_2.onReceivedSslError.overload('android.webkit.WebView', 'android.webkit.WebResourceRequest', 'android.webkit.WebResourceError').implementation = function (obj1, obj2, obj3) {
console.log('[+] Bypassing Android WebViewClient {2}');
};
} catch (err) {
console.log('[-] Android WebViewClient {2} pinner not found');
//console.log(err)
}

// Apache Cordova WebViewClient //
//
try {
var CordovaWebViewClient_Activity = Java.use('org.apache.cordova.CordovaWebViewClient');
CordovaWebViewClient_Activity.onReceivedSslError.overload('android.webkit.WebView', 'android.webkit.SslErrorHandler', 'android.net.http.SslError').implementation = function (obj1, obj2, obj3) {
console.log('[+] Bypassing Apache Cordova WebViewClient');
obj3.proceed();
};
} catch (err) {
console.log('[-] Apache Cordova WebViewClient pinner not found');
//console.log(err);
}

// Boye AbstractVerifier //
///
try {
var boye_AbstractVerifier = Java.use('ch.boye.httpclientandroidlib.conn.ssl.AbstractVerifier');
boye_AbstractVerifier.verify.implementation = function (host, ssl) {
console.log('[+] Bypassing Boye AbstractVerifier: ' + host);
};
} catch (err) {
console.log('[-] Boye AbstractVerifier pinner not found');
//console.log(err);
}

});

}, 0);

启动frida进行hook指定APP的包名

frida -U -f com.example.safehttps -l hook.js --no-pause

image.png

可以看到开启burp抓包成功。

5.开启双向校验

双向校验顾名思义也就是服务器也要对客户端进行证书校验,在刚才客户端校验服务端的基础上添加一直被校验的逻辑在里面。

首先ttt.com所在的nginx服务器要开启双向认证
image.png

开启客户端的校验后,在浏览器进行访问,会发现返回400,没有被请求的SSL证书发送,是因为浏览器正常请求不会携带证书信息去请求ttt.com
image.png

那么如何携带客户端的证书,就要利用burp来操作,将ttt.com的证书添加到TLS客户证书
image.png

这时再访问
image.png

在APP中进行绑定客户端的证书文件,一般是p12格式文件,会放在assets目录下或者raw目录下,client.p12会有一个密钥内置在代码中,需要找到才能添加进burp中。
image.png

这个在反编译后的目录下也能找到,通常在assets或者res/raw目录下查找,但是再导入burp这一步是需要证书密码的,比如上图能明显看到密码是123456,但是找不到证书密码怎么办,可以看一下目录下是否存在lib文件夹,如果存在的话极大可能是将密码写进so层了,这就需要你会IDA反汇编获取证书密钥了,这部分在此不详细阐述,感兴趣的朋友可以先去研究一下。
image.png

APP双向校验验证

服务器校验客户端的证书ClientSSLSocketFactory,服务端将客户端的证书进行绑定。

TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
trustManagerFactory.init((KeyStore) null);
TrustManager[] trustManagers = trustManagerFactory.getTrustManagers();
if (trustManagers.length != 1 || !(trustManagers[0] instanceof X509TrustManager)) {
    throw new IllegalStateException("Unexpected default trust managers:" + Arrays.toString(trustManagers));
}
trustManager = (X509TrustManager) trustManagers[0];

OkHttpClient client = new OkHttpClient.Builder()
        .sslSocketFactory(Objects.requireNonNull(ClientSSLSocketFactory.getSocketFactory(getApplicationContext())), Objects.requireNonNull(trustManager))
        .hostnameVerifier(new HostnameVerifier() {
            @Override
            public boolean verify(String hostname, SSLSession session) {
                //强行返回true 即验证成功
                return true;
            }
}).build();

public class ClientSSLSocketFactory  {
    private static final String KEY_STORE_PASSWORD = "123456"; // 证书密码
    private static InputStream client_input;

    public static SSLSocketFactory getSocketFactory(Context context) {
        try {
            //客户端证书
            client_input = context.getResources().getAssets().open("client.p12");
            SSLContext sslContext = SSLContext.getInstance("TLS");
            KeyStore keyStore = KeyStore.getInstance("PKCS12");
            keyStore.load(client_input, KEY_STORE_PASSWORD.toCharArray());
            KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
            keyManagerFactory.init(keyStore, KEY_STORE_PASSWORD.toCharArray());
            sslContext.init(keyManagerFactory.getKeyManagers(), null, new SecureRandom());
            return sslContext.getSocketFactory();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                client_input.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }
}

双向校验时,要将SSLPinning与服务器校验客户端证书的模块同时开启。

对其就行绕过,需要先启动Frida进行hook,然后勾选上客户端证书,才可以请求成功。如下图所示:
image.png

没勾选就会请求失败,出现400 Bad Request,和浏览器无代理时请求的结果一样,如下图:
image.png

此时burp代理日志显示如下,SSL请求失败
image.png

WebView证书校验

webview也是一种请求方式,相当于页面的跳转或嵌入,请求的结果会显示在主屏幕上。

对于webview证书校验,有些可以找到的脚本不一定有绕过,所以在使用的过程中要查看是否含有webview的关键信息

这里我使用的是DroidSSLUnpinning

使用效果如下:
image.png

image.png

此时的APP绑定场景为:OKhttp请求为双向校验,webview为SSLPinning校验。所以在图中的上面一行是okhttp的请求结果,下面的是webview的请求结果,此脚本双向校验仍然可以绕过。

如果说webview再添加了客户端校验,那么在反编译apk后,需要找到webview访问域名的证书密钥,再安装进burp中即可。

6.ssl_logger通杀

至此,我们可以绕过证书绑定,抓APP发出的https包了,然而上述的证书解绑hook工具仅仅是通过hook了几种绑定证书的API,不适用于新出现或者非主流的证书绑定技术。这时,就需要神器ssl_logger

ssl_logger是用来解密SSL流量的工具,也是一款基于frida的hook工具,通过hook libssl库中的SSL_read、SSL_write等函数来实现流量解密,由于底层的实现会调用这几个函数来封装,所以可以直接解出流量数据。
image.png

r0capture是r0ysue大佬在其基础上进行改进的一款工具。
image.png

由于ssl_logger是适用于MAC和linux操作系统,所以我选择在kali上进行hook实现双向校验的app
image.png

打开抓到的1.pcap包
image.png
image.png

从图中可以看出成功的获取到了信息,是不是感觉这个工具特别神,但是看pcap的包总归不如看burp的一目了然,这个工具就这一点不太友好。所以用哪个看你心情

7.eBPF hook 免CA证书

ecapture:eBPF HOOK uprobe实现的各种用户态进程的数据捕获,无需改动原程序。这个工具也是通过hook了libssl库中SSL_writeSSL_read这两个关键的SSL加密函数的返回值,拿到明文信息,通过ebpf map传递给用户进程。在APP中,如果遇到场景是burp抓包时出现证书报错,我觉得可以尝试一下用这个工具直接curl访问进行抓包。eBPF hook也是最近才发现的hook方法,值得我们去深入探索。

我这里用的是作者v0.1.3版本发布的工具,使用效果如下:
image.png

8.总结

在依靠系统或默认浏览器校验证书的情况下,导入burp证书为用户证书是可以抓https包的

当app支持的最小API为24(Android 7.0)或以上时,默认情况下app只信任系统级别的证书,需要把burp变为系统证书

自签名证书作为系统证书时,有效期最长不超过825天,用户证书则没有限制

开启证书校验的APP在使用burp抓包时会报certtificate_unknown等错误

使用frida hook绕过双向证书校验时,必须要将客户端的p12文件导入burp中

一些脚本仍绕不过可以使用ssl_logger或者逆向代码进行分析验证逻辑,再有针对性的绕过

p12文件的密钥如果在so层,需要会用IDA进行静态分析lib下的so文件获取关键密钥

看完本篇文章之后,相信你再面对抓不到包的APP或者是https请求也不会手足无措了。

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