Cracking Cortana: The Dangers of Flawed Voice Assistants

Security vs. convenience is a delicate balance to strike with new technology designed to make our lives easier. Vulnerabilities in voice assistants like Microsoft's Cortana and Amazon's Alexa are perfect examples of how the rush to simplify can cause complicated problems down the road.

Consider Cortana, which is enabled by default in Windows 10. Cortana was built to facilitate vocal interaction with laptops, desktops, smartphones, and IoT devices running Microsoft's newest OS, and it's becoming more common in the enterprise as organizations deploy Windows 10 across their environments. The rollout is leaving holes in enterprise defense because Cortana, like other voice assistants, prioritizes users' comfort over security.

Amichai Shulman, cofounder and CTO of Imperva, has spent the past year exploring the technology, infrastructure, and protocols of voice assistants with his colleague, security researcher Tal Be'ery. He says Cortana serves as a weak interface over the otherwise secure Windows operating system and has discovered multiple vulnerabilities to support this.

"Cortana takes a stable environment, reasonably secured, and adds this new type of interface on top of it," Shulman explains. He and Be'ery will present their findings on Cortana flaws in August at Black Hat USA in a session entitled "Open Sesame: Picking Locks with Cortana."

Want Data? All You Have to Do Is Ask

It didn't take long for the researchers to learn the default setting in Windows 10 lets anyone communicate with Cortana – even when the machine is locked. "We started looking for methods to bypass the lock mechanism using voice," says Shulman.

They first found the Voice of Esau (VoE) exploit, which let attackers take over a locked Windows 10 device by combining voice commands with network manipulation to put a malicious payload on a target machine.

VoE was patched by Microsoft in August 2017; still, Shulman believed there were more vulnerabilities to be uncovered. He continued his research, testing concepts like vocal malware along with students at Technion, the Israel Institute of Technology. There are local and Internet-based extensions for Cortana; a whole set of protocols and APIs that can be attacked, he says.

One of the flaws they discovered, dubbed Open Sesame, will be the core focus of their Black Hat session. CVE-2018-8140 was recently addressed in Microsoft's June Patch Tuesday update.

Open Sesame is more powerful than VoE, he says, and allows attackers to take over a locked Windows 10 machine and execute arbitrary code. Exploiting this vulnerability would let anyone view sensitive files, browse online, download and launch arbitrary executables from the Internet, and in some cases gain elevated privileges. A threat actor wouldn't need external code to pull this off, so antivirus and IPS tools wouldn't pick up on the attack.

"There are a number of scenarios where close proximity attacks are being used – computers in hotel rooms, airport security attacks … just give your locked computer to someone to inspect and in a matter of seconds that computer can be compromised," Shulman explains.

A Conversation on Convenience

The reason behind these vulnerabilities is twofold, Shulman says. For starters, Microsoft tried to pitch a new interface, built on accessibility and comfort, onto a secured multi-purpose computing environment. "When you do that, there are glitches," he points out.

It is beneficial to have some commands available on a locked machine. Asking about the weather, for example, is benign. However, it's tricky to enable certain functionalities while denying operations that could potentially compromise the machine.

The second problem: Microsoft's assistant is more than a voice interface. Shulman calls it "an intent resolution engine." Cortana takes natural language input and conveys it into an action performed by the machine. However, it accepts both written and spoken commands. Once the system is invoked with "Hey Cortana," an attacker can enter keyboard input and execute code on a locked device.

As part of their discussion, Shulman and Be'ery will address defense mechanisms for protecting against these types of attacks. One lesson, at least for enterprise environments, is to make sure the enhanced interface is off by default. Vendors don't like to launch new services and not have them active by default, Shulman says, but in the workplace "it's the prudent thing to do."

The team will demonstrate the Open Sesame vulnerability at Black Hat There are three more Cortana vulnerabilities Shulman hopes to discuss in their presentation but they are waiting on confirmation before they can publicly share more details.

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