Example - 1

This code temporarily raises the program's privileges to allow creation of a new user folder.

// #avoid CWE-22 and CWE-78// 
print('Usernames cannot contain invalid characters')return False

raisePrivileges()os.mkdir('/home/' + username)lowerPrivileges()

print('Unable to create new user directory for user:' + username)return False
if invalidUsername(username):try:except OSError:return Truedef makeNewUserDir(username):

While the program only raises its privilege level to create the folder and immediately lowers it again, if the call to os.mkdir() throws an exception, the call to lowerPrivileges() will not occur. As a result, the program is indefinitely operating in a raised privilege state, possibly allowing further exploitation to occur.

Example - 2

The following code calls chroot() to restrict the application to a subset of the filesystem below APP_HOME in order to prevent an attacker from using the program to gain unauthorized access to files located elsewhere. The code then opens a file specified by the user and processes the contents of the file.

chroot(APP_HOME);chdir("/");FILE* data = fopen(argv[1], "r+");...

Constraining the process inside the application's home directory before opening any files is a valuable security measure. However, the absence of a call to setuid() with some non-zero value means the application is continuing to operate with unnecessary root privileges. Any successful exploit carried out by an attacker against the application can now result in a privilege escalation attack because any malicious operations will be performed with the privileges of the superuser. If the application drops to the privilege level of a non-root user, the potential for damage is substantially reduced.

Example - 3

This application intends to use a user's location to determine the timezone the user is in:

locationClient = new LocationClient(this, this, this);locationClient.connect();Location userCurrLocation;userCurrLocation = locationClient.getLastLocation();setTimeZone(userCurrLocation);

This is unnecessary use of the location API, as this information is already available using the Android Time API. Always be sure there is not another way to obtain needed information before resorting to using the location API.

Example - 4

This code uses location to determine the user's current US State location.

First the application must declare that it requires the ACCESS_FINE_LOCATION permission in the application's manifest.xml:

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

During execution, a call to getLastLocation() will return a location based on the application's location permissions. In this case the application has permission for the most accurate location possible:

locationClient = new LocationClient(this, this, this);locationClient.connect();Location userCurrLocation;userCurrLocation = locationClient.getLastLocation();deriveStateFromCoords(userCurrLocation);

While the application needs this information, it does not need to use the ACCESS_FINE_LOCATION permission, as the ACCESS_COARSE_LOCATION permission will be sufficient to identify which US state the user is in.