Video Aircraft instrument landing systems (ILS) are susceptible to radio signal spoofing using off-the-shelf equipment, boffins have found, calling into question the adequacy of aviation cybersecurity.
In a research paper titled "Wireless Attacks on Aircraft Instrument Landing Systems," scheduled to be presented at the 28th USENIX Security Symposium in August, computer scientists Harshad Sathaye, Domien Schepers, Aanjhan Ranganathan, and Guevara Noubir demonstrate that it's possible to interfere with ILS data in real-time, potentially causing aircraft to discontinue a landing approach ("go around") or miss the landing area entirely in a low-visibility situation.
The researchers, based at Northeastern University in Boston, USA, are also scheduled to demonstrate some of their findings today at ACM WiSec 2019.
In a phone interview with The Register, Aanjhan Ranganathan, assistant professor in the Khoury College of Computer Sciences, said he was hesitant to characterize the attack techniques discussed in the paper as capable of causing a crash.
"If a human is completely out of the loop, then this is possible," he told us today, adding that could become more of an issue in the years to come if fully automated landings become common.
But the more immediate concern is that malicious individuals may use this technique to disrupt airport operations by tricking pilots into aborting landing attempts. "You can cause something like denial of service," he said.
ILS helps pilots make an instrument approach when the landing strip is not visible. It provides both vertical and lateral guidance and defines three major categories, CAT I, CAT II and CAT III, based the decision height at which missed approach maneuvers must be undertaken when the runway cannot be seen.
The attacks described in the paper are of particular concern during CAT III operations, where the decision height is low, making it possibly too late to regain altitude and try to land again.
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ILS, the paper explains, is the most common precision approach system used by commercial aircraft today. It's not the only assistive landing system – there's the Microwave Landing System (MLS), the Transponder Landing System (TLS), the Ground Based Augmentation Landing System (GLS), and the Joint Precision Approach and Landing System (JPALS). Nor is it the only source of navigation data. But its ability to resist cyberattacks is still a matter of significant concern.
"Given the heavy reliance on ILS and instruments in general, malfunctions and adversarial interference can be catastrophic especially in autonomous approaches and flights," the paper says.
The Northeastern University eggheads have designed two wireless attacks on ILS. The first they call the "overshadow attack," which involves sending specific ILS signals at a high power level to overpower legitimate ILS signals. The second they call a single-tone attack that interferes with a legitimate ILS signal through the transmission of a lower power frequency tone that alters the plane's course deviation indicator needle.
The attacks were tested with commercial available software-defined radio equipment (USRP B210s), an attacker control unit (a laptop running Ubuntu Linux with four submodules, including a spoofing zone detector, offset correction algorithm, legitimate signal generator, and attacker signal generator), a commercial aviation grade handheld navigation receiver, and the X-Plane 11 flight simulator (to avoid injuries and remain within the law, which prohibits open air transmission of ILS signals).
That's several thousand dollars in gear but Ranganathan said the necessary tech could be had for six or seven hundred dollars. Generating a signal that's powerful enough to have an effect avionics systems at 5,000 feet might be a problem, he said, but that's easy enough to achieve with a few car batteries.
The effect of the attacks is to misdirect ILS, which could disrupt a landing attempt or even cause a crash if the pilot fails to recognize the plane is landing off the runway. The researchers have made this video, which illustrates in a computer simulation how their spoofing technique would, ideally, work:
While encryption can help secure aviation systems, it's not a complete fix. "Cryptography will prevent spoofing but won't stop record-and-replay attacks," Ranganathan said.
As far as mitigation go, systems like GPS can help, though GPS too has been shown to be vulnerable to spoofing. Ranganathan's answer for now is that humans need to remain in the loop.
"It's a very open problem and the only way to do this is two-way communication," he said. ®