PIXHELL - Data Exfiltration Through Screen Noise

This post is meant as a discussion around some of the challenges the attack has in the real world, and how to overcome them (both while attacking and defending).

Reference (attack described in detail): (thehackernews.com) - New PIXHELL Attack Exploits Screen Noise to Exfiltrates Data from Air-Gapped Computers

Summary

The PIXHELL attack is a side-channel technique targeting air-gapped computers by using pixel patterns on LCD screens to generate acoustic signals. These signals, created by exploiting coil whine and capacitor noise in the screen's components, are used to exfiltrate data without needing audio hardware. The attack can be detected by observing screen anomalies, but it can also operate covertly when users are absent.

Challenges of the PIXHELL Attack

While PIXHELL offers a novel approach to exfiltrating data, it faces significant challenges:

1. Noise Interference: The acoustic signals emitted by the screen’s components can be easily disrupted by environmental noise, which makes the transmission of data less reliable in noisy settings.
2. Slow Data Rates: Since the data is encoded in acoustic signals, the transmission rate is considerably slower compared to traditional wireless methods, limiting the amount of data that can be exfiltrated in a given time.
3. Proximity Requirements: PIXHELL requires the attacker to be physically close to the target system in order to capture the acoustic signals. This proximity requirement limits the practicality of the attack in certain scenarios.

These challenges reduce the attack's effectiveness, but overcoming them (as described later) could significantly enhance its real-world potential.

Overcoming Challenges in the PIXHELL Attack

To improve the efficiency and practicality of the PIXHELL attack, several enhancements can be made to mitigate key challenges:

1. Noise Interference: Environmental sounds can disrupt the transmission of acoustic signals. To counter this, attackers could:

- Use higher-frequency signals (closer to 22 kHz), where less ambient noise is present.

- Implement advanced noise filtering techniques to isolate and enhance the target acoustic signals, reducing the impact of interference from other devices or human activities.

2. Slow Data Rates: Acoustic signals inherently transmit data at a slower rate compared to traditional wireless methods, limiting the amount of data that can be exfiltrated. To address this:

- Data compression could be employed before encoding the data into pixel transitions. Compression would reduce the size of the data payload, speeding up the exfiltration process.

- Utilize error-correcting codes that ensure the reliability of data transmission, allowing the attack to maintain accuracy even with minimal data throughput.

- Parallel Transmission: Display multiple regions of the screen with pixel patterns to transmit multiple data streams simultaneously. This would enhance the data rate while remaining within acoustic transmission limits.

3. Proximity Requirement: PIXHELL typically requires the receiver to be close to the compromised system, as acoustic signals degrade over distance. To extend the operational range:

- Amplification techniques could be applied to both the generation and reception of the signals, boosting the strength of the acoustic waves emitted by the screen.

- Relay Devices: Intermediate compromised devices could be strategically placed to capture and forward the acoustic signals to a remote location. For example, a compromised smartphone near the system could relay the data to an attacker far away, bypassing proximity limitations.

By addressing these challenges, the PIXHELL attack could become a more reliable and versatile tool for attackers to extract sensitive information from air-gapped systems, further demonstrating the need for stronger defenses.

Defending Against PIXHELL

So what are some of the possibilities to defend against this attack?

• Acoustic Jammers: Deploy jammers that disrupt the specific frequency range (0-22 kHz) used by PIXHELL. These devices can block the acoustic signals from reaching any nearby receivers.

• Monitor Audio Emissions: Continuously scan the audio spectrum of the environment for abnormal or unauthorized acoustic signals. Tools could be developed to detect unusual sound patterns generated by screen components.
• Physical and Device Access Control: Limit access to the air-gapped system area. Ensure that external devices, such as smartphones or laptops, are prohibited or thoroughly monitored to prevent potential receivers from capturing emitted signals.
• Screen and Component Hardening: Consider using displays with fewer capacitors and inductors prone to coil whine or acoustic leakage. Alternatively, shield screens to minimize unintended emissions.
• Off-Hours Monitoring: Since the PIXHELL attack is most effective when users are absent, use security cameras or sensors to monitor screens and detect abnormal pixel patterns that may signal an ongoing exfiltration.
• Data Encryption: Even if an attacker captures the acoustic signals, using robust encryption on sensitive data ensures it remains undecipherable, adding an extra layer of defense.

By employing a combination of these measures, entities can significantly reduce the risk posed by PIXHELL or similar side-channel attacks.

Example attack showed at:

PIXHELL Attack: Leaking Sensitive Information from Air-Gap Computers via ‘Singing Pixels’ (youtube.com)