A feature in newer Android phones and tablets is compromising user privacy by broadcasting a list of the most recently connected wi-fi networks while the device is in sleep mode, the Electronic Frontier Foundation has found.
The preferred network offload (PNO) feature, found in Android versions from Honeycomb (Android 3.1) onwards, allows devices to connect to wi-fi networks while in low power in order to extend battery life. The feature prioritises less power-hungry wi-fi connections over cellular connections.
But the feature is broadcasting a list of the 15 most recent wi-fi networks the device was connected to even while the device is in sleep mode, the EFF found, meaning anyone within wi-fi range of the device is able to access the connection history and map the user's recent physical location.
“Wi-fi devices that are not actively connected to a network can send out messages that contain the names of networks they’ve joined in the past in an effort to speed up the connection process,” the EFF found.
The offending code is the open source wpa_supplicant application which is used by Android to manage wi-fi, the EFF said. It said Google yesterday submitted a patch to the application which fixed the issue, ahead of Google integrating the fix into the downstream Android code.
“We take the security of our users’ location data very seriously and we’re always happy to be made aware of potential issues ahead of time. Since changes to this behavior would potentially affect user connectivity to hidden access points, we are still investigating what changes are appropriate for a future release," Google told the EFF.
Not all Android devices running Honeycomb are affected - the EFF said it tested 28 devices and found Google Nexus, Motorola Droid and HTC One models among others leaked the data, while other newer devices including Samsung Galaxy S3 and S4 models did not.
iOS devices were in the clear, but the EFF found all OS X laptops and many Windows 7 laptops were affected. It did not test Windows Phone or BlackBerry operating systems.
"Desktop OSes will need to be fixed, but because our laptops are not usually awake and scanning for networks as we walk around, locational history extraction from them requires considerably more luck or targeting."
The digital rights group advised users to turn off the "keep wi-fi on during sleep" option within the device's advanced wi-fi settings as a temporary solution, but warned the workaround is not available on all devices.
Other users would need to manually clear network history to remain secure.