Air gap (networking)


An air gap, air wall or air gapping is a network security measure employed on one or more computers to ensure that a secure computer network is physically isolated from unsecured networks, such as the public Internet or an unsecured local area network. It means a computer or network has no network interfaces connected to other networks, with a physical or conceptual air gap, analogous to the air gap used in plumbing to maintain water quality.

Use in classified settings

An "air-gapped" computer or network is one that has no network interfaces, either wired or wireless, connected to outside networks. Many computers, even when they are not plugged into a wired network, have a wireless network interface controller and are connected to nearby wireless networks to access the Internet and update software. This represents a security vulnerability, so air-gapped computers either have their wireless interface controller permanently disabled or physically removed. To move data between the outside world and the air-gapped system, it is necessary to write data to a physical medium such as a thumbdrive, and physically move it between computers. Physical access is easier to control than an electronic network interface, which can be attacked at any time from the exterior insecure system and, if malware infects the secure system, can be used to export secure data.
In environments where networks or devices are rated to handle different levels of classified information, the two disconnected devices or networks are referred to as "low side" and "high side", "low" being unclassified and "high" referring to classified, or classified at a higher level. This is also occasionally referred to as "red" and "black". Access policies are often based on the Bell–LaPadula confidentiality model, where data can be moved low-to-high with minimal security measures, while high-to-low requires much more stringent procedures to ensure protection of the data at a higher level of classification.
The concept represents nearly the maximum protection one network can have from another. The only way to transfer data between the outside world and the air-gapped system is to copy data on a removable storage medium such as a removable disk or USB flash drive and physically carry the storage to the other system. This access can be more easily controlled. The upside to this is that such a network can generally be regarded as a closed system, unable to be accessed from the outside world. The downside is that transferring information to be analyzed by computers on the secure network is extraordinarily labor-intensive, often involving human security analysis of prospective programs or data to be entered onto air-gapped networks and possibly even human manual re-entry of the data following security analysis.
Sophisticated computer viruses for use in cyberwarfare, such as Stuxnet and agent.btz have been designed to infect air-gapped systems by exploiting security holes related to the handling of removable media. The possibility of using acoustic communication has also been demonstrated by researchers. Researchers have also demonstrated the feasibility of data exfiltration using FM frequency signals.

Examples

Examples of the types of networks or systems that may be air gapped include:
Many of these systems have since added features that connect them to the public internet, and are no longer effectively air gapped, including thermostats with internet connections and automobiles with Bluetooth, Wi-Fi and cellular phone connectivity.

Limitations

Limitations imposed on devices used in these environments may include a ban on wireless connections to or from the secure network, or similar restrictions on EM leakage from the secure network through the use of TEMPEST or a Faraday cage.
Despite a lack of direct connection to other systems, air-gapped networks have been shown to be vulnerable to attack in various circumstances.
Scientists in 2013 demonstrated the viability of air gap malware designed to defeat air gap isolation using acoustic signaling. Shortly after that, network security researcher Dragos Ruiu's BadBIOS received press attention.
In 2014, researchers introduced "AirHopper", a bifurcated attack pattern showing the feasibility of data exfiltration from an isolated computer to a nearby mobile phone, using FM frequency signals.
In 2015, BitWhisper, a covert signaling channel between air-gapped computers using thermal manipulations was introduced. BitWhisper supports bidirectional communication and requires no additional dedicated peripheral hardware.
Later in 2015, researchers introduced GSMem, a method for exfiltrating data from air-gapped computers over cellular frequencies. The transmission - generated by a standard internal bus - renders the computer into a small cellular transmitter antenna.
ProjectSauron malware discovered in 2016 demonstrates how an infected USB device can be used to remotely leak data off of an air-gapped computer. The malware remained undetected for 5 years and relied on hidden partitions on a USB drive not visible to Windows as a transport channel between the air-gapped computer and a computer connected to the internet, presumably as a way to share files between the two systems.
NFCdrip was the name given to the discovery of stealthy data exfiltration through NFC radio abuse and signal detection in 2018. Although NFC enables devices to establish effective communication by bringing them within a few centimeters of each other, researchers showed that it can be abused to transmit information at a much longer range than expected - up to 100 meters.
In general, malware can exploit various hardware combinations to leak sensitive information from air-gapped systems using "". These hardware combinations use a number of different mediums to bridge the air-gap, including: acoustic, light, seismic, magnetic, thermal, and radio-frequency.