Android P will also Prevent Idle Background Apps from Recording you via Microphone

By | 20th February 2018

The next major version of Android, Android P, might be weeks away, but each passing day brings new breadcrumbs. One of the focuses of Android P appears to be protecting user privacy. Yesterday, we wrote about how Android P will impose limitations on “idle” background apps that request access to the camera. Following up on that, we also discovered an Android Open Source Project (AOSP) commit merged that same day that prevents idle background apps from accessing the microphone.

We can imagine that this news might be shocking to some of you. Yes, technically any app that you gave permission to access your device’s microphones could have been running in the background and recording anything you say, although Android Oreo’s limitations on background services may have indirectly made that a bit harder to get away with. Still, the idea that an app, idling away in the background, could be secretly recording you is a scary premise straight out of Black Mirror—and that’s why Google is working to fix that.

What’s changing in Android P?

Here’s how it’ll work: When an app, identified by its UID—the unique, unchanging identifier the Android system assigns at install time—enters an idle state, Android’s audio system won’t allow it to record audio. (In this case, “idle” refers to the idle Doze state when background apps’ access to CPU and network-intensive services is restricted.) Instead of writing data from the microphone to a file, it’ll report empty data (a string of zeros in the byte array). Once the app becomes active again (i.e., exits Doze mode), it’ll start recording real data.

It might sound (no pun intended) a little bit convoluted, but the goal is to protect privacy. Idle apps recording junk audio will prevent a hypothetical malicious app from becoming quickly aware that its access has been cut off and thus prevent them from recording ambient noise, private conversations, and your surroundings surreptitiously.

Why does it matter?

Apps that secretly access your phone’s microphone aren’t just the paranoid delusions of security researchers. Late last year, The New York Times reported that more than 1,000 popular Android apps listen for ad-tracking audio signals through device microphones.

Android 6.0 Marshmallow introduced a permissions system that blocks apps from accessing the microphone (and other sensors) by default. But it’s a one-time deal: after you’ve granted an app permission, there’s nothing to prevent it from abusing that permission in the future. Revoking permissions, in fact, is a bit of a chore: You have to head to the Android Settings menu, tap Apps, scroll to the app and select it, tap App Permissions, and find the relevant permission.

With any luck, Android P will do the hard work for you.