Cautious users put a piece of tape over their webcam. Truly paranoid ones worry about their devices’ microphones — some even crack open their computers and phones to disable or remove those audio components so they can’t be hijacked by hackers. Now one group of Israeli researchers has taken that game of spy-versus-spy paranoia a step further, with malware that converts your headphones into makeshift microphones that can slyly record your conversations.
Researchers at Israel’s Ben Gurion University have created a piece of proof-of-concept code they call “Speake(a)r,” designed to demonstrate how determined hackers could find a way to surreptitiously hijack a computer to record audio even when the device’s microphones have been entirely removed or disabled. The experimental malware instead repurposes the speakers in earbuds or headphones to use them as microphones, converting the vibrations in air into electromagnetic signals to clearly capture audio from across a room.
“People don’t think about this privacy vulnerability,” says Mordechai Guri, the research lead of Ben Gurion’s Cyber Security Research Labs. “Even if you remove your computer’s microphone, if you use headphones you can be recorded.”
It’s no surprise that earbuds can function as microphones in a pinch, as dozens of how-to YouTube videos demonstrate. Just as the speakers in headphones turn electromagnetic signals into sound waves through a membrane’s vibrations, those membranes can also work in reverse, picking up sound vibrations and converting them back to electromagnetic signals. (Plug a pair of mic-less headphones into an audio input jack on your computer to try it.)
But the Ben Gurion researchers took that hack a step further. Their malware uses a little-known feature of RealTek audio codec chips to silently “retask” the computer’s output channel as an input channel, allowing the malware to record audio even when the headphones remain connected into an output-only jack and don’t even have a microphone channel on their plug. The researchers say the RealTek chips are so common that the attack works on practically any desktop computer, whether it runs Windows or MacOS, and most laptops.
The eavesdropping attack should only matter to those who have already gone a few steps down the rabbit-hole of obsessive counter-intelligence measures. In the modern age of cybersecurity, fears of having your computer’s mic surreptitiously activated by stealthy malware are increasingly mainstream: Guri points to the photo that revealed earlier this year that Mark Zuckerberg had put tape over his laptop’s microphone. In a video for Vice News, Edward Snowden demonstrated how to remove the internal mic from a smartphone. Even the NSA’s information assurance division suggests “hardening” PCs by disabling their microphones, and repair-oriented site iFixit’s Kyle Wiens showed MacWorld in July how to physically disable a Macbook mic. None of those techniques—short of disabling all audio input and output from a computer—would defeat this new malware. (Guri says his team has so far focused on using the vulnerability in RealTek chips to attack PCs, though. They have to determine which other audio codec chips and smartphones might be vulnerable to the attack, They have to determine which other audio codec chips and smartphones might be vulnerable to the attack, but believe other chips and devices are likely also susceptible.)
In their tests, the researchers tried the audio hack with a pair of Sennheiser headphones. They found that they could record from as far as 20 feet away—and even compress the resulting recording and send it over the internet, as a hacker would—and still distinguish the words spoken by a male voice. “It’s very effective,” says Guri. “Your headphones do make a good, quality microphone.
There’s no simple software patch for the eavesdropping attack, Guri says. The property of RealTek’s audio codec chips that allows a program to switch an output channel to an input isn’t an accidental bug so much as a dangerous feature, Guri says, and one that can’t be easily fixed without redesigning and replacing the chip in future computers.