DRD04-J. Do not log sensitive information

Android provides capabilities for an app to output logging information and obtain log output. Applications can send information to log output using the android.util.Log class. To obtain log output, applications can execute the logcat command.

To log output

The android.util.Log class allows a number of possibilities:

Example:

Log.v("method", Login.TAG + ", account=" + str1);
Log.v("method", Login.TAG + ", password=" + str2);

To obtain log output

Declare READ_LOGS permission in the manifest file so that an app can read log output:

AndroidManifest.xml:

<uses-permission android:name="android.permission.READ_LOGS"/>

Call logcat from an application:

Process mProc = Runtime.getRuntime().exec(
    new String[]{"logcat", "-d", "method:V *:S$Bc`W^(B)"});

BufferedReader mReader = new BufferedReader(
    new InputStreamReader(proc.getInputStream()));

Prior to Android 4.0, any application with READ_LOGS permission could obtain all the other applications' log output. After Android 4.1, the specification of READ_LOGS permission has been changed. Even applications with READ_LOGS permission cannot obtain log output from other applications.

However, by connecting an Android device to a PC, log output from other applications can be obtained.

Therefore, it is important that applications do not send sensitive information to log output.

Noncompliant Code Example

Facebook SDK for Android contained the following code which sends Facebook access tokens to log output in plain text format.

Log.d("Facebook-authorize", "Login Success! access_token="
      + getAccessToken() + " expires="
      + getAccessExpires());

Source: http://blog.parse.com/2012/04/10/discovering-a-major-security-hole-in-facebooks-android-sdk/

Noncompliant Code Example

Here is another example. A weather report for Android sent a user's location data to the log output as follows:

I/MyWeatherReport( 6483): Re-use MyWeatherReport data
I/ ( 6483): GET JSON: http://example.com/smart/repo_piece.cgi?arc=0&lat=26.209026&lon=127.650803&rad=50&dir=-999&lim=52&category=1000

If a user is using Android OS 4.0 or before, other applications with READ_LOGS permission can obtain the user's location information without declaring ACCESS_FINE_LOCATION permission in the manifest file.

Proof of Concept

Example code of obtaining log output from a vulnerable application is as follows:

final StringBuilder slog = new StringBuilder();

try {
  Process mLogcatProc;
  mLogcatProc = Runtime.getRuntime().exec(new String[]
      {"logcat", "-d", "LoginAsyncTask:I APIClient:I method:V *:S" });

  BufferedReader reader = new BufferedReader(new InputStreamReader(
      mLogcatProc.getInputStream()));

  String line;
  String separator = System.getProperty("line.separator");

  while ((line = reader.readLine()) != null) {
    slog.append(line);
    slog.append(separator);
  }
  Toast.makeText(this, "Obtained log information", Toast.LENGTH_SHORT).show();

} catch (IOException e) {
  // handle error
}

TextView tView = (TextView) findViewById(R.id.logView);
tView.setText(slog);

Applicability

Applications should make sure that they do not send sensitive information to log output. If the app includes a third party library, the developer should make sure that the library does not send sensitive information to log output. One common solution is for an application to declare and use a custom log class, so that log output is automatically turned on/off based on Debug/Release. Developers can use ProGuard to delete specific method calls. This assumes that the method contains no side effects.

This rule is a special case of FIO13-J. Do not log sensitive information outside a trust boundary.

Risk Assessment

Logging sensitive information can leak sensitive information to malicious apps.

Automated Detection

Automatic detection of the use of logging facilities trivial. It is not feasible to automatically determine whether the data being logged is sensitive.

Related Vulnerabilities

• Facebook SDK for Android: http://readwrite.com/2012/04/10/what-developers-and-users-can#awesm=~o9iqZAMlUPshPu
• JVN#23328321 Puella Magi Madoka Magica iP for Android vulnerable to information disclosure
• JVN#86040029 Weathernews Touch for Android stores location information in the system log file
• JVN#33159152 Loctouch for Android information management vulnerability
• JVN#56923652 Monaca Debugger for Android information management vulnerability

Related Guidelines

Bibliography