Malware can infect system using Inaudible Audio signals

Pierluigi Paganini December 04, 2013

German researchers demonstrated how a malware can infect system in air gapped networks and transfer stolen data using Inaudible Audio signals.

The shocking news that it is possible to infect a computer with Inaudible Audio signals is circulating within the security community has been circulating for several weeks between denials and confirmations.

In October the security researcher Dragos Ruiu described a malware codenamed badBIOS characterized by the capability to infect targeted machines using sound waves as transmission vector, immediate was the skeptical reaction of the world security community.

Even if a computer system is isolated from the Internet, and any if the use of any mobile devices (e.g. USB stick, mobile storage) is not allowed, an attacker could infect the target just using Inaudible Audio signals.

The proof of concept has been provided by German scientists at the Fraunhofer Institute for Communication, Information Processing and Ergonomics, that designed malware prototype, the scientists also have published a paper describing on how malware can be designed to cross the air gap by transmitting data through common speakers and recording it via microphone. The malicious code relies on network stack originally developed for underwater communication and the propagation of the signal exploit a software-defined modem based on the GNU Radio project.

The computers operates as a mesh network where each node can send or receive audio emanation, and implements routing activities sending data to the next hop in the chain before it’s received by the attacker.

“The concept of a covert acoustical mesh network renders many conventional security concepts useless, as acoustical communications are usually not considered,” states the paper.

The fake sense of security that isolating a network is possible to protect a network was dismantled by the news.

The methods attack open the way to scaring scenarios, let’s think of the ability to infect any ability air gapped network within a critical infrastructure exploiting Inaudible Audio signals as a vector to spread malicious code for sabotage or for cyber espionge.

The attack scenario is described in the paper with the below statement:

“The infected victim sends all recorded keystrokes to the covert acoustical mesh network. Infected drones forward the keystroke information inside the covert network till the attacker is reached, who is now able to read the current keyboard input of the infected victim from a distant place.”

The researchers demonstrated that the malware is able to transfer data at a very low transfer rate, 20 bits /Sec, that anyway are enough to transfer sensitive data such as user’s credential or any other personal information.

The researchers also demonstrated how to use sound waves to send keystroke information to a network-connected computer, which then sent the data back to the attacker via email.

Malware exploit Inaudible Audio signals2

How to mitigate a similar attack?

Some basic countermeasures can be implemented to protect systems against malware transferred via Inaudible Audio signals:

Switching off the audio input and output devices from the system.
Employ audio filtering that blocks high-frequency ranges.
Using an Audio Intrusion Detection Guard.

The paper describes is very intriguing because it incorporates the Dragos Ruiu’s allegations, it remark the principle that is possible to infect a “disconnected system” exploiting a different channel for malware propagation.

Michael Hanspach and Michael Goetz confirmed that there is no connection between their paper and badBIOS, Hanspach said their attack is feasible today because the utilized techniques are well documented.

“If we were able to come up with this research with very few people, time and budget (and with good intentions), so would be larger groups (maybe with a different intention),” “Therefore, anyone working in a security critical context should be thinking about protection measures.” Hanspach said via email to the Threatpost.

Let’s wait for a security solution, meantime security managers of critical computing systems are advised.

Pierluigi Paganini

(Security Affairs – Malware, Inaudible Audio signals)

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