Alexa and Google voice assistants app exploits left it vulnerable to eavesdropping

Security researchers developed skills for both the Google Home and the Amazon Echo that could eavesdrop on people.

Chris Monroe/CNET

There are already privacy concerns when it comes to smart speakers in the home — but now security researchers have found that malicious apps designed to eavesdrop can sneak through Google’s and Amazon’s vetting processes. 

On Sunday, Security Research Labs disclosed their findings after developing eight voice apps that could listen in on people’s conversations through Amazon’s Echo and Google’s Nest devices. All of the apps passed through the companies’ reviews for third-party apps. The research was first reported by CNET sister site ZDNet

Amazon and Google didn’t respond to requests for comment. 

Voice assistants present a privacy headache, since the devices that use them are essentially internet-connected microphones in your home, delivering your conversations to servers at Amazon, Apple or Google. All three companies have been criticized over their reviews processes, which used human contractors to listen to select conversations with the voice assistants. 

They’ve also taken steps to improve their privacy settings. Apple and Google now require people to opt in to be a part of the reviews program. Amazon also sought to improve its privacy settings available for Alexa after the backlash.

But security researchers found there’s still a lot of room for improvement with security on voice assistants.  

The eavesdropping apps worked by taking advantage of silence. The researchers developed horoscope apps, and when prompted, would respond with an error message. But instead of ending the recording process like an Alexa or Google Assistant skill usually does, it kept listening in the background. 

That’s because the developers simulated silence by inserting the unicode character sequence “�. ” (U+D801, dot, space). That character cannot be pronounced, but both Alexa and the Google Home’s text-to-speech AI attempts to process it anyway, leaving a silent gap during which it continues listening even after a person thinks the device is finished with the task. 

That recorded conversation isn’t just sent to Amazon and Google’s servers, it’s also sent to the third-party developers as well. 

The security researchers also demonstrated that they could use these malicious apps to trick people into giving up their passwords. After an extended period of silence, the skills could make the voice assistants say, “An important security update is available for your device. Please say start update followed by your password.”

Hacks like these have happened before for Amazon’s Alexa. In April 2018, security researchers found an error in Alexa’s code where malicious apps could keep the skill listening indefinitely, essentially letting any third-party app eavesdrop on people. 

Like how Security Research Labs hid their eavesdropping in horoscope apps, the previous vulnerability was tucked away in a calculator app. 

The researchers said they’ve disclosed the vulnerabilities to Amazon and Google earlier this year, and the apps have since been removed.