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Slides of our Blackhat USA 2018 talk:
Many new devices are trying to fit into our life seamlessly. As a result, there’s a quest for a “universal access methods” for all devices. Voice activation seems to be a natural candidate for the task and many implementations for it surfaced in recent years. A few notable examples are Amazon’s Alexa, Google’s Assistant and Microsoft’s Cortana.
The problem starts when these “Universal” access methods, aimed for maximal comfort, meet the very “specific” use-case of the enterprise environment which requires comfort to be balanced with other aspects, such as security. Microsoft Cortana is used on Mobile and IoT devices, but also in the enterprise computers as it comes enabled by default with Windows10 and always ready to respond to users’ commands even when the machine is locked.
Allowing interaction with a locked machine is a dangerous architectural decision, and earlier this year, we exposed the Voice of Esau (VoE) exploit for a Cortana vulnerability. The VoE exploit allowed attackers to take over a locked Windows10 machine by combining voice commands and network fiddling to deliver a malicious payload to the victim machine.
In this presentation, we will reveal the “Open Sesame” vulnerability, a much more powerful vulnerability in Cortana that allows attackers to take over a locked Windows machine and execute arbitrary code. Exploiting the “Open Sesame” vulnerability attackers can view the contents of sensitive files (text and media), browse arbitrary web sites, download and execute arbitrary executables from the Internet, and under some circumstances gain elevated privileges. To make matters even worse, exploiting the vulnerability does not involve ANY external code, nor shady system calls, hence making code focused defenses such as Antivirus, Anti-malware and IPS blind to the attack.
We would conclude by suggesting some defense mechanisms and compensating controls to detect and defend against such attacks.