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. The name arises from the technique of creating a network that is physically separated (with a conceptual air gap) from all other networks.
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" (classified) and "black" (unclassified). To move data from the high side to the low side, it is necessary to write data to a physical medium, and move it to a device on the latter network. Traditionally based on the Bell–LaPadula confidentiality model, data can be moved low-to-high with minimal processes, 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 (save turning the device off). It is not possible for network packets to "leap" across the air gap from one network to another. The upside to this is that such a network can generally be regarded as a closed system (in terms of information, signals, and emissions security), unable to be accessed from the outside world. The downside is that transferring information (from the outside world) 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.
Computer viruses such as Stuxnet and agent.btz have been known to bridge the gap 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 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 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.
Further, 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.
In general, malware can exploit various hardware combinations to leak sensitive information from air-gapped systems using "air-gap covert channels". These hardware combinations use a number of different mediums to bridge the air-gap, including: acoustic, light, seismic, magnetic, thermal, and radio-frequency.
For example, top-secret data might be kept on a different computer than data classified merely as sensitive material. Sometimes, for a worker to access information, up to six different computers can be on a single desk. That type of security is called, in typical intelligence community jargon, an air gap.
In high-security situations, various forms of data often must be kept off production networks, due to possible contamination from nonsecure resources — such as, say, the Internet. So IT admins must build enclosed systems to house that data — stand-alone servers, for example, or small networks of servers that aren't connected to anything but one another. There's nothing but air between these and other networks, hence the term air gap, and transferring data between them is done the old-fashioned way: moving disks back and forth by hand, via 'sneakernet'.
Stock exchange internal network computer systems are so sensitive that they are “air gapped” and not attached to the internet, in order to protect them from attack, intrusion, or other malicious acts by third party adversaries.
Industrial internal network computer systems are so sensitive that they are “air gapped” and neither attached to the internet nor insecurely connects to the corporate network, in order to protect them from attack, intrusion, or other malicious acts by third party adversaries.
(...Boeing...) wouldn't go into detail about how (...it...) is tackling the issue but says it is employing a combination of solutions that involves some physical separation of the networks, known as air gaps, and software firewalls.
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