CVE-2018-11567 in Echo
Summary
by MITRE
Prior to 2018-04-27, the reprompt feature in Amazon Echo devices could be misused by a custom Alexa skill. The reprompt feature is designed so that if Alexa does not receive an input within 8 seconds, the device can speak a reprompt, then wait an additional 8 seconds for input; if the user still does not respond, the microphone is then turned off. The vulnerability involves empty output-speech reprompts, custom wildcard ("gibberish") input slots, and logging of detected speech. If a maliciously designed skill is installed, an attacker could obtain transcripts of speech not intended for Alexa to process, but simply spoken within the device's hearing range.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability CVE-2018-11567 represents a significant privacy and security flaw in Amazon Echo devices that existed prior to April 27, 2018, specifically within the reprompt functionality of the Alexa voice assistant system. This issue stems from how the device handles voice input processing when users fail to respond to Alexa's initial prompts, creating an unintended data collection mechanism that could be exploited by malicious actors. The reprompt feature was designed as a user experience enhancement to give users additional time to respond to voice commands, but the implementation contained a critical oversight that allowed unauthorized access to ambient audio content. The vulnerability operates through a combination of three specific technical elements that when orchestrated together create the exploitable condition.
The technical flaw manifests through the interaction between empty output-speech reprompts, custom wildcard input slots, and the device's speech logging mechanisms. When a malicious Alexa skill is installed, it can configure the reprompt feature to use empty speech responses while simultaneously setting up wildcard input slots that capture any spoken content within the device's hearing range. The device's logging system, which normally captures only intended voice commands, becomes inadvertently activated to record ambient speech that would otherwise remain unprocessed. This creates a situation where the microphone continues to record and log audio content even when users are speaking about topics unrelated to Alexa commands, effectively turning the device into an unintended surveillance tool. The vulnerability is categorized under CWE-200, Information Exposure, and aligns with ATT&CK technique T1566 for social engineering through malicious voice commands.
The operational impact of this vulnerability extends beyond simple privacy concerns to encompass potential data harvesting and surveillance capabilities that could be exploited by threat actors. An attacker with access to a victim's Echo device could deploy a malicious skill that systematically collects ambient conversations, potentially capturing sensitive personal information, business discussions, or confidential communications. The vulnerability particularly affects users who may not be aware that their device is continuously recording and logging audio content beyond the scope of intended voice interactions. This represents a significant deviation from the expected behavior of voice assistant devices, where users reasonably expect that only their explicit voice commands will be processed and stored. The exposure could be particularly severe in corporate environments where sensitive meetings or discussions might be inadvertently recorded and logged by compromised devices.
Mitigation strategies for this vulnerability required immediate action from Amazon to update the device firmware and modify the reprompt functionality to prevent the exploitation pattern. Users needed to ensure their devices were updated to the latest software version that addressed the specific vulnerability in the reprompt handling logic. Additionally, users should carefully review and manage the permissions granted to Alexa skills, particularly those that request access to voice input or speech processing capabilities. The fix implemented by Amazon likely involved modifying how the device handles empty reprompt responses and ensuring that wildcard input slots do not inadvertently trigger continuous speech logging. Organizations should implement comprehensive security policies regarding smart device usage and regularly audit the skills and permissions configured on voice assistant devices within their environments. The vulnerability serves as a reminder of the importance of secure coding practices in IoT devices and the need for continuous security monitoring of connected devices that process personal information.