CVE-2021-38549 in MHUB500 (Glowworm)
Summary
by MITRE • 08/12/2021
MIRACASE MHUB500 USB splitters 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.
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Analysis
by VulDB Data Team • 08/16/2021
This vulnerability represents a sophisticated side-channel attack targeting consumer electronics devices that demonstrates the intersection of physical security and electromagnetic interference. The MIRACASE MHUB500 USB splitter, specifically version 2021-08-09 and earlier, contains a critical flaw that transforms a simple power indicator LED into an information leakage vector. The vulnerability stems from the direct connection between the power indicator LED and the device's power line, creating a physical correlation between power consumption and light intensity that can be exploited by adversaries. This represents a classic example of a timing channel attack where the temporal characteristics of power consumption directly map to audio signal variations. The attack methodology relies on the principle that audio signals driving connected speakers cause fluctuations in power consumption, which are then reflected in the LED's brightness variations. The specific use case requires the device to supply power to audio-output equipment, making this vulnerability particularly concerning for environments where sensitive communications occur. This attack vector operates under the framework of passive side-channel analysis and falls under the category of electromagnetic information leakage.
The technical implementation of this vulnerability exploits the fundamental relationship between electrical power consumption and optical emission in LED components. The power indicator LED functions as a simple photometric sensor that directly reflects the device's power draw, which varies proportionally with audio signal amplitude when driving speakers. The electro-optical sensor captures these minute variations in light intensity, while a telescope amplifies the optical signal to enable detection at distance. The attack requires specialized equipment including high-sensitivity optical sensors, telescopic optics, and signal processing capabilities to extract meaningful audio information from the captured light variations. The correlation between audio signals and power consumption creates a direct information channel that bypasses traditional network security measures. This vulnerability specifically relates to CWE-310, which addresses cryptographic weakness, and more precisely maps to CWE-312, which covers cleartext storage of sensitive data, though in this case the data is exposed through physical rather than digital means. The attack demonstrates how physical components can serve as unintended information channels, a concept that aligns with the broader principles of physical security and electromagnetic interference.
The operational impact of this vulnerability extends far beyond simple information disclosure, as it enables remote eavesdropping on audio communications without requiring any network access or device compromise. Attackers can recover speech signals from connected speakers using only optical equipment positioned at a distance from the vulnerable device, making this attack particularly dangerous in corporate boardrooms, government facilities, or any environment where sensitive conversations occur. The attack is persistent and can be conducted repeatedly without leaving digital traces, making it extremely difficult to detect or prevent through conventional security monitoring. The vulnerability affects devices that are commonly deployed in office environments and homes, creating a widespread attack surface. Organizations using these devices in sensitive environments face potential compromise of classified information, proprietary discussions, and personal communications. The attack does not require any modification of the device or network infrastructure, making it accessible to adversaries with basic optical equipment and signal processing capabilities. This vulnerability directly impacts the confidentiality aspect of information security and represents a significant gap in physical security design.
Mitigation strategies for this vulnerability require both hardware and operational approaches to address the fundamental design flaw in the device's power indicator implementation. The most effective solution involves redesigning the power indicator circuitry to isolate the LED from the main power line or implementing filtering mechanisms that prevent audio signal correlation with power consumption variations. Device manufacturers should consider using optically isolated power indicators or implementing digital power monitoring that does not directly reflect analog power variations. Organizations should conduct risk assessments to identify vulnerable devices in their environments and implement physical security measures such as limiting access to areas where sensitive communications occur. The use of Faraday cages or electromagnetic shielding around vulnerable devices can prevent optical signal capture, though this requires careful implementation to avoid interfering with device functionality. Network administrators should consider the physical security implications of device deployment and implement policies that restrict the use of vulnerable devices in sensitive areas. This vulnerability highlights the need for comprehensive security design that considers not only digital threats but also physical side-channel attacks, aligning with the principles of defense in depth and secure by design methodologies. The attack pattern described corresponds to techniques found in the ATT&CK framework under the T1046 category for network service scanning, though in this case the attack is conducted through physical rather than digital means.