CVE-2021-38543 in UE330 (Glowworm)
Summary
by MITRE • 08/12/2021
TP-Link UE330 USB splitter devices through 2021-08-09, in certain specific use cases in which the device supplies power to audio-output equipment, allow remote attackers to recover speech signals from an LED on the device, via a telescope and an electro-optical sensor, aka a "Glowworm" attack. We assume that the USB splitter supplies power to some speakers. The power indicator LED of the USB splitter is connected directly to the power line, as a result, the intensity of the USB splitter's power indicator LED is correlative to its power consumption. The sound played by the connected speakers affects the USB splitter's power consumption and as a result is also correlative to the light intensity of the LED. By analyzing measurements obtained from an electro-optical sensor directed at the power indicator LED of the USB splitter, we can recover the sound played by the connected speakers.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 08/16/2021
The vulnerability identified as CVE-2021-38543 represents a sophisticated side-channel attack against TP-Link UE330 USB splitter devices that operates through electromagnetic interference and optical signal analysis. This security flaw exploits the direct electrical connection between the device's power indicator LED and the power line supplying audio equipment, creating a covert channel that can be exploited by remote attackers. The vulnerability specifically manifests when the USB splitter device provides power to audio-output equipment such as speakers, establishing a pathway for information leakage through the physical characteristics of the device's power consumption patterns.
The technical mechanism underlying this vulnerability stems from the fundamental electrical properties of the device's power indicator LED, which serves as a direct visual representation of the device's power consumption. According to the vulnerability analysis, the power indicator LED is directly connected to the power line rather than being isolated through proper filtering or regulation circuits, creating an unintended data transmission channel. When audio signals are played through connected speakers, the power consumption of the USB splitter device fluctuates in direct correlation with the audio waveform, causing corresponding variations in the LED's light intensity. This relationship between audio input and LED output creates a form of electromagnetic side-channel information leakage that can be captured and decoded.
The attack vector described in this vulnerability operates through a sophisticated technique that combines optical sensing with signal processing to reconstruct audio information from visual light variations. Attackers can utilize a telescope combined with an electro-optical sensor positioned to capture the power indicator LED's light emissions, effectively creating a "Glowworm" attack that leverages the device's power indicator as an unintended communication medium. This approach aligns with the principles outlined in the Common Weakness Enumeration (CWE) category CWE-310, which addresses cryptographic weaknesses and information leakage through side channels. The attack methodology demonstrates how physical device design flaws can create security vulnerabilities that bypass traditional network-based security measures.
The operational impact of this vulnerability extends beyond simple information disclosure to represent a significant threat to privacy and security in environments where audio equipment is connected to affected USB splitters. The ability to recover speech signals from a remote location using optical sensors and signal processing techniques represents a form of active surveillance that can be employed against any device in the affected product line. This vulnerability affects devices manufactured through 2021-08-09, indicating that the design flaw was present in a substantial number of units and potentially represents a widespread security risk for organizations and individuals using these devices in sensitive environments.
The implications of this vulnerability align with the MITRE ATT&CK framework's concept of information gathering and reconnaissance activities, where adversaries exploit physical device characteristics to extract sensitive information. This attack demonstrates how physical security considerations must be integrated into device design processes, particularly for products that interface with electrical power systems and audio equipment. The vulnerability highlights the importance of proper electrical isolation and filtering techniques in consumer electronics to prevent unintended information leakage through power line characteristics and LED indicators. Organizations should consider implementing physical security measures and device placement strategies to mitigate the risk of such optical attacks while also ensuring that device manufacturers incorporate security-by-design principles to prevent similar vulnerabilities in future product iterations.