Privacy Violation: Screen Caching

iOS will automatically take a screenshot before an app is backgrounded (i.e. hitting the "Home" button when the app is active). This may compromise user privacy if sensitive information is on display while this occurs.

The identified UIViewController subclass does not implement the appropriate methods used to hide screen elements before iOS caches the screen's contents. This will reveal any sensitive information that has been entered within input controls before an app is backgrounded.

Example 1: Input entered into iOS text controls may be stored in a screenshot taken when an app is backgrounded (i.e. the "Home" button is pressed while the app is active).

ViewController.h
...

@property (nonatomic, retain) IBOutlet UITextField *ssnField;

...

The code in Example 1 indicates that the app utilizes an input control designed to collect sensitive information. As iOS takes a screenshot of the active view of an app when it is backgrounded in order to improve animation performance, any information displayed in such input controls during the background event may be cached within an image saved to the file system. Because these screen cache screenshots are stored on the device, if the device is lost, they may be recovered, thereby revealing any sensitive information contained within.

Private data can enter a program in a variety of ways:

- Directly from the user in the form of a password or personal information.

- Accessed from a database or other data store by the application.

- Indirectly from a partner or other third party.

- Retrieved from mobile data stores including: address book, snapped photos, geolocation, configuration files, archived SMS messages, etc.

Sometimes data that is not labeled as private can have a privacy implication in a different context. For example, student identification numbers are usually not considered private because there is no explicit and publicly-available mapping to an individual student's personal information. However, if a school generates student identification based on student social security numbers, then the identification numbers should be considered private.

Security and privacy concerns often seem to compete with each other. From a security perspective, you should record all important operations so that any anomalous activity can later be identified. However, when private data is involved, this practice can create additional risk.

Although there are many ways in which private data can be handled unsafely, a common risk stems from misplaced trust. Programmers often trust the operating environment in which a program runs, and therefore believe that it is acceptable to store private information on the file system, in the registry, or in other locally-controlled resources. However, even if access to certain resources is restricted, it does not guarantee that the individuals who do have access can be trusted with certain data. For example, in 2004, an unscrupulous employee at AOL sold approximately 92 million private customer email addresses to a spammer marketing an offshore gambling web site [1].

In response to such high-profile exploits, the collection and management of private data is becoming increasingly regulated. Depending on its location, the type of business it conducts, and the nature of any private data it handles, an organization may be required to comply with one or more of the following federal and state regulations:

- Safe Harbor Privacy Framework [3]

- Gramm-Leach Bliley Act (GLBA) [4]

- Health Insurance Portability and Accountability Act (HIPAA) [5]

- California SB-1386 [6]

Despite these regulations, privacy violations continue to occur with alarming frequency.