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Android证书信任问题与大表哥.html
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<html>
<head>
<title>Android证书信任问题与大表哥 - 瘦蛟舞</title>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
</head>
<body>
<h1>原文地址:<a href="http://drops.wooyun.org/tips/3296">http://drops.wooyun.org/tips/3296</a></h1>
<p>
<h2>0x00 起因</h2>
<hr />
<p>1、近期icloud.com、yahoo.com、apple.com遭遇到大规模劫持</p>
<p> <a target="_blank" href="http://www.wooyun.org/bugs/wooyun-2014-080117">WooYun: Yahoo雅虎在国内访问遭遇SSL中间人攻击（被替换为自签名证书）</a> </p>
<p>2、乌云平台、CVE都收到大量有关Android APP信任所有证书的漏洞</p>
<p> <a target="_blank" href="http://www.wooyun.org/bugs/wooyun-2014-079358">WooYun: 国内绝大部分Android APP存在信任所有证书漏洞</a> </p>
<p>3、老外写有关大表哥的文章中提到MITM时360浏览器不提示证书错误</p>
<p><a href="http://www.computerworld.com/article/2836084/chinese-big-brother-launches-nationwide-attack-on-icloud.html">http://www.computerworld.com/article/2836084/chinese-big-brother-launches-nationwide-attack-on-icloud.html</a></p>
<p>之前信任证书问题一直都有被提到，但是普遍不受大家重视，因为这个漏洞是利用是需要场景的：MITM（中间人攻击 Man-in-the-middle attack）。一般情况下MITM相对其他攻击是比较少见的，如果有良好的上网习惯如不接入不受信任的网络，那就更少可能受此类攻击了。但是近期发生的MITM据传是在核心骨干网BGP上做了改动所以劫持范围非常之广，真是防不胜防呀，你被劫持了么？</p>
<!--more-->
<h2>0x01 科普</h2>
<hr />
<p><strong>https&&ssl</strong></p>
<p>为了提高网站的安全性，一般会在比较敏感的部分页面采用https传输，比如注册、登录、控制台等。像Gmail、网银、icloud等则全部采用https传输。https/ssl主要起到两个作用：网站认证、内容加密传输和数据一致性。经CA签发的证书才起到认证可信的作用，所有有效证书均可以起到加密传输的作用。</p>
<p><strong>数字证书</strong></p>
<p>主要在互联网上的用于身份验证的用途。 安全站点在获得CA（Certificate Authority数字证书认证机构）认证后，获得一个数字证书，以此来标识其合法身份的真实性。数字证书主要分为服务器证书和客户端证书。服务器证书（SSL证书）用来进行身份验证和通信的加密，客户端证书主要用于身份验证和电子签名。找CA申请证书是要收费的。</p>
<p><strong>自签名证书</strong></p>
<p>非CA颁发的证书，通过自签名的方式得到的证书。通常Web浏览器会显示一个对话框，询问您是否希望信任一个自签名证书。这个是不用花钱的。</p>
<p><strong>中间人攻击</strong></p>
<p>是指攻击者与通讯的两端分别创建独立的联系，并交换其所收到的数据，使通讯的两端认为他们正在通过一个私密的连接与对方直接对话，但事实上整个会话都被攻击者完全控制。在中间人攻击中，攻击者可以拦截通讯双方的通话并插入新的内容。在许多情况下这是很简单的。</p>
<h2>0x02 分析</h2>
<hr />
<p>如果自己简单的实现android webview加载网页，如果直接访问可信证书的站点是可以正常显示，但是如果访问自签名的证书的站点就会显示notfound的页面。(写本文时apple.com以及apple.com.cn处于劫持状态)</p>
<p><img src="http://static.wooyun.org/drops/20141023/20141023115732webview.jpg" alt="" /></p>
<p>logcat会输出网页显示不安全的内容</p>
<pre><code>Web Console:The page displayed insecure content!
</code></pre>
<p>功能健全的手机浏览器访问自签名证书的站点会如下提醒</p>
<p><img src="http://static.wooyun.org/drops/20141023/20141023115731mUC.jpg" alt="" /></p>
<p>在PC端如果访问自签名证书的站点则会出现如下图左侧的提醒</p>
<p><img src="http://static.wooyun.org/drops/20141023/20141023115731360.jpg" alt="" /></p>
<p>为解决<code>javax.net.ssl.SSLPeerUnverifiedException: No peer certificate</code>的异常，开发者往往会采用以下的错误解决方案。如此是浏览器应用采用此类解决方案，那么风险就更大了。</p>
<p>覆盖google默认的证书检查机制</p>
<pre><code>#!java
class bv
implements X509TrustManager
{
bv(bu parambu) {}
public void checkClientTrusted(X509Certificate[] paramArrayOfX509Certificate, String paramString) {// Do nothing -> accept any certificates}
public void checkServerTrusted(X509Certificate[] paramArrayOfX509Certificate, String paramString) {// Do nothing -> accept any certificates}
public X509Certificate[] getAcceptedIssuers()
{
return null;
}
}
</code></pre>
<p>信任所有主机名</p>
<pre><code>#!java
public static HttpClient getNewHttpClient() {
try {
//获得密匙库
KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
trustStore.load(null, null);
SSLSocketFactory sf = new SSLSocketFactoryEx(trustStore);
//信任所有主机名
sf.setHostnameVerifier(SSLSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER);
HttpParams params = new BasicHttpParams();
HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
HttpProtocolParams.setContentCharset(params, HTTP.UTF_8);
SchemeRegistry registry = new SchemeRegistry();
registry.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
registry.register(new Scheme("https", sf, 443));
ClientConnectionManager ccm = new ThreadSafeClientConnManager(params, registry);
return new DefaultHttpClient(ccm, params);
} catch (Exception e) {
return new DefaultHttpClient();
}
}
</code></pre>
<p>empty HostnameVerifier</p>
<pre><code>#!java
HostnameVerifier hv = new HostnameVerifier() {
@Override
public boolean verify(String hostname, SSLSession session) {
// Always return true -> Accespt any host names
return true;
}
};
</code></pre>
<p>忽略WebView证书错误继续加载</p>
<pre><code>#!java
myWebView.setWebViewClient(new WebViewClient(){
@Override
public void onReceivedError(WebView view, int errorCode,
String description, String failingUrl) {
// TODO Auto-generated method stub
super.onReceivedError(view, errorCode, description, failingUrl);
}
@Override
public void onReceivedSslError(WebView view,
SslErrorHandler handler, SslError error) {
// TODO Auto-generated method stub
handler.proceed();
}});
</code></pre>
<p>其实早在14年2月<a href="http://drops.wooyun.org/papers/959">窃听风暴： Android平台https嗅探劫持漏洞</a>文中就有提到android平台的app因为覆盖google默认的证书检查机制（X509TrustManager）之后没有对证书进行应有的安全性检查，直接接受了所有异常的https证书，不提醒用户存在安全风险，也不终止这次危险的连接。文中对证书域名检查（HostnameVerifier）部分没有细说。</p>
<p>上文有提到PC版的360浏览器访问被劫持网站居然没有证书错误提示，让人很不敢相信。加上最近android app 证书问题频发，猜想是否有可能一些手机浏览器也会有此类漏洞了。测试过程中发现360手机浏览器、和搜狗浏览器存在此风险。</p>
<p>百度和遨游轻松检测出证书异常</p>
<p><img src="http://static.wooyun.org/drops/20141023/20141023115732baidu.jpg" alt="" /></p>
<p><img src="http://static.wooyun.org/drops/20141023/20141023115731aoyou.jpg" alt="" /></p>
<p>而360和搜狗直接加载进入了被劫持的网站。</p>
<p><img src="http://static.wooyun.org/drops/20141023/20141023115731m360.jpg" alt="" /></p>
<p><img src="http://static.wooyun.org/drops/20141023/20141023115732sougou.jpg" alt="" /></p>
<p>反编译查看遨游浏览器的代码，针对证书异常做了处理</p>
<p><img src="http://static.wooyun.org/drops/20141023/20141023115732true.jpg" alt="" /></p>
<p><img src="http://static.wooyun.org/drops/20141023/20141023115731mismatch.jpg" alt="" /></p>
<p>而搜狗浏览器则是做了证书信任所有主机名不当处理</p>
<p><img src="http://static.wooyun.org/drops/20141023/20141023115732trust.jpg" alt="" /></p>
<p>关键字：checkServerTrusted、setHostnameVerifier、ALLOW_ALL_HOSTNAME_VERIFIER、X509TrustManager、onReceivedSslError</p>
<h2>0x03 对比</h2>
<hr />
<p>对主流手机浏览器进行了横向对比，测试对象包括：firefox、chrome、UC浏览器、搜狗浏览器、百度浏览器、360安全浏览器、欧鹏浏览器、遨游云浏览器、猎豹浏览器。</p>
<p>测试方法：手机访问<a href="https://example.com/">https://example.com/</a>,观察是否有安全提醒。(update:此方法已经无效.)</p>
<p>未做提醒直接加载网页：360安全浏览器、猎豹浏览器、搜狗浏览器</p>
<p>正常做出安全提醒：firefox、chrome、UC浏览器、百度浏览器、欧鹏浏览器、遨游云浏览器</p>
<h2>0x04 建议</h2>
<hr />
<p>开发者：</p>
<p>1、非浏览器app，有钱申请ca证书没钱在客户端中添加证书,切勿信任所有证书。</p>
<p>2、浏览器app，严格按照客户端校验服务器证书流程处理:</p>
<ul>
<li>查看证书是否过期 </li>
<li>CA是否可靠 </li>
<li>CA的公钥能否正确解开服务器证书的CA数字签名，即证书的签名值 </li>
<li>服务器证书上的域名是否和服务器的实际域名相匹配</li>
</ul>
<p>3、建议使用setHostnameVerifier(SSLSocketFactory.STRICT_HOSTNAME_VERIFIER)</p>
<p>一个SSLSocketFactory的example</p>
<pre><code>#!java
java public class SecureSocketFactory extends SSLSocketFactory {
private static final String LOG_TAG = "SecureSocketFactory";
private final SSLContext sslCtx;
private final X509Certificate[] acceptedIssuers;
/**
* Instantiate a new secured factory pertaining to the passed store. Be sure to initialize the
* store with the password using <a class="__cf_email__" href="/cdn-cgi/l/email-protection" data-cfemail="374c775b5e595c">[email protected]</a><script data-cfhash='f9e31' type="text/javascript">/* <![CDATA[ */!function(t,e,r,n,c,a,p){try{t=document.currentScript||function(){for(t=document.getElementsByTagName('script'),e=t.length;e--;)if(t[e].getAttribute('data-cfhash'))return t[e]}();if(t&&(c=t.previousSibling)){p=t.parentNode;if(a=c.getAttribute('data-cfemail')){for(e='',r='0x'+a.substr(0,2)|0,n=2;a.length-n;n+=2)e+='%'+('0'+('0x'+a.substr(n,2)^r).toString(16)).slice(-2);p.replaceChild(document.createTextNode(decodeURIComponent(e)),c)}p.removeChild(t)}}catch(u){}}()/* ]]> */</script> java.security.KeyStore#load(java.io.InputStream,
* char[])} method.
*
* @param store The key store holding the certificate details
* @param alias The alias of the certificate to use
*/
public SecureSocketFactory(KeyStore store, String alias)
throws
CertificateException,
NoSuchAlgorithmException,
KeyManagementException,
KeyStoreException,
UnrecoverableKeyException {
super(store);
// Loading the CA certificate from store.
final Certificate rootca = store.getCertificate(alias);
// Turn it to X509 format.
InputStream is = new ByteArrayInputStream(rootca.getEncoded());
X509Certificate x509ca = (X509Certificate) CertificateFactory.getInstance("X.509").generateCertificate(is);
AsyncHttpClient.silentCloseInputStream(is);
if (null == x509ca) {
throw new CertificateException("Embedded SSL certificate has expired.");
}
// Check the CA's validity.
x509ca.checkValidity();
// Accepted CA is only the one installed in the store.
acceptedIssuers = new X509Certificate[]{x509ca};
sslCtx = SSLContext.getInstance("TLS");
sslCtx.init(
null,
new TrustManager[]{
new X509TrustManager() {
@Override
public void checkClientTrusted(X509Certificate[] chain, String authType) throws CertificateException {
}
@Override
public void checkServerTrusted(X509Certificate[] chain, String authType) throws CertificateException {
Exception error = null;
if (null == chain || 0 == chain.length) {
error = new CertificateException("Certificate chain is invalid.");
} else if (null == authType || 0 == authType.length()) {
error = new CertificateException("Authentication type is invalid.");
} else {
Log.i(LOG_TAG, "Chain includes " + chain.length + " certificates.");
try {
for (X509Certificate cert : chain) {
Log.i(LOG_TAG, "Server Certificate Details:");
Log.i(LOG_TAG, "---------------------------");
Log.i(LOG_TAG, "IssuerDN: " + cert.getIssuerDN().toString());
Log.i(LOG_TAG, "SubjectDN: " + cert.getSubjectDN().toString());
Log.i(LOG_TAG, "Serial Number: " + cert.getSerialNumber());
Log.i(LOG_TAG, "Version: " + cert.getVersion());
Log.i(LOG_TAG, "Not before: " + cert.getNotBefore().toString());
Log.i(LOG_TAG, "Not after: " + cert.getNotAfter().toString());
Log.i(LOG_TAG, "---------------------------");
// Make sure that it hasn't expired.
cert.checkValidity();
// Verify the certificate's public key chain.
cert.verify(rootca.getPublicKey());
}
} catch (InvalidKeyException e) {
error = e;
} catch (NoSuchAlgorithmException e) {
error = e;
} catch (NoSuchProviderException e) {
error = e;
} catch (SignatureException e) {
error = e;
}
}
if (null != error) {
Log.e(LOG_TAG, "Certificate error", error);
throw new CertificateException(error);
}
}
@Override
public X509Certificate[] getAcceptedIssuers() {
return acceptedIssuers;
}
}
},
null
);
setHostnameVerifier(SSLSocketFactory.STRICT_HOSTNAME_VERIFIER);
}
@Override
public Socket createSocket(Socket socket, String host, int port, boolean autoClose)
throws IOException {
injectHostname(socket, host);
Socket sslSocket = sslCtx.getSocketFactory().createSocket(socket, host, port, autoClose);
// throw an exception if the hostname does not match the certificate
getHostnameVerifier().verify(host, (SSLSocket) sslSocket);
return sslSocket;
}
@Override
public Socket createSocket() throws IOException {
return sslCtx.getSocketFactory().createSocket();
}
/**
* Pre-ICS Android had a bug resolving HTTPS addresses. This workaround fixes that bug.
*
* @param socket The socket to alter
* @param host Hostname to connect to
* @see <a href="https://code.google.com/p/android/issues/detail?id=13117#c14">https://code.google.com/p/android/issues/detail?id=13117#c14</a>
*/
private void injectHostname(Socket socket, String host) {
try {
if (Integer.valueOf(Build.VERSION.SDK) >= 4) {
Field field = InetAddress.class.getDeclaredField("hostName");
field.setAccessible(true);
field.set(socket.getInetAddress(), host);
}
} catch (Exception ignored) {
}
}
}
</code></pre>
<p>用户：使用安全性较好的app</p>
<h2>0x05 参考</h2>
<hr />
<p><a href="http://drops.wooyun.org/tips/2775" title="http://drops.wooyun.org/tips/2775">http://drops.wooyun.org/tips/2775</a></p>
<p><a href="http://drops.wooyun.org/papers/959" title="http://drops.wooyun.org/papers/959">http://drops.wooyun.org/papers/959</a></p>
<p><a href="http://developer.android.com/reference/javax/net/ssl/HttpsURLConnection.html" title="http://developer.android.com/reference/javax/net/ssl/HttpsURLConnection.html">http://developer.android.com/reference/javax/net/ssl/HttpsURLConnection.html</a></p>
<p><a href="http://developer.android.com/reference/javax/net/ssl/X509TrustManager.html">http://developer.android.com/reference/javax/net/ssl/X509TrustManager.html</a></p>
<p><a href="http://developer.android.com/training/articles/security-ssl.html">http://developer.android.com/training/articles/security-ssl.html</a></p>
<p><a href="http://developer.android.com/reference/org/apache/http/conn/ssl/SSLSocketFactory.html">http://developer.android.com/reference/org/apache/http/conn/ssl/SSLSocketFactory.html</a></p> </p>
</body>
</html>