SPEAKE(a)R: Transforming Audio Devices into Covert Microphones

In the realm of cybersecurity, the potential to covertly transform headphones, earphones, and simple earbuds into eavesdropping microphones presents a significant threat. This paper introduces 'SPEAKE(a)R,' a sophisticated malware capable of exploiting this vulnerability in PCs. By manipulating the hardware and software configurations, particularly through a process known as jack retasking, attackers can reconfigure audio jacks from output to input, thereby converting connected audio devices into recording microphones.

## Technical Background

The fundamental principle that allows this transformation is the bidirectional nature of audio devices. Speakers and microphones operate on similar principles but in reverse; speakers convert electrical signals into sound, while microphones do the opposite. Modern audio chipsets, such as those from Realtek, support jack retasking, allowing software to change the function of audio ports. This capability, although documented, is not widely known or utilized.

## Malware Design and Implementation

The SPEAKE(a)R malware consists of both user-level processes and kernel-level drivers. The malware can stealthily reconfigure audio jacks, turning headphones into microphones even when the computer's built-in microphone is disabled or absent. This transformation is achieved by sending specific configuration commands to the audio codec via the HD audio interface.

## Evaluation and Results

Experiments demonstrate that headphones can record human speech with intelligible quality from distances up to nine meters. Various speech quality measures, such as SNR (Signal-to-Noise Ratio) and PESQ (Perceptual Evaluation of Speech Quality), were used to assess the effectiveness of the headphones as microphones. Although the audio quality is inferior to standard microphones, the recordings are still intelligible.

## Attack Scenarios

The attack scenarios primarily involve computers without microphones or those with disabled microphones. In such cases, malware can use connected headphones to record conversations, bypassing traditional security measures aimed at protecting audio privacy.

## Countermeasures

To mitigate this threat, both hardware and software countermeasures are suggested. Hardware solutions include using one-way speakers or on-board amplifiers to prevent reverse audio capture. Software solutions involve disabling audio codecs in BIOS/UEFI settings or enforcing strict jack retasking policies through kernel drivers. Additionally, anti-malware systems can monitor and block unauthorized retasking operations.

## Conclusion

The SPEAKE(a)R malware highlights a critical vulnerability in modern PCs, where audio devices can be repurposed for espionage. This paper underscores the importance of awareness and proactive security measures to protect against such covert surveillance threats.