The sound of an emergency alert siren can be a nightmare soundtrack to the millions who live in areas subject to hurricanes, tornados, earthquakes, or other natural disasters. A recently disclosed vulnerability in the emergency warning system used by San Francisco and other municipalities could allow a threat actor to take control of the system, sound false alarms, or block legitimate warnings.
While the vendor - ATI - says it has now patched the so-called SirenJack vulnerability, an unencrypted protocol, the process of its discovery could have implications for other locations.
Balint Seeber, a researcher with Bastille, began researching San Francisco's warning siren system shortly after moving to the city in 2016. Noticing poles with sirens attached scattered throughout the city, and noting that the hardware for the sirens included radio antennae, Seeber was curious about the system's security.
After realizing that there was a system test every Tuesday, Seeber first began looking for the system's radio frequency. "I started every week, capturing and analyzing large chunks of the radio spectrum with a view to trying to find this one unknown signal amongst hundreds, maybe thousands, of signals across the spectrum and that took some time," he says.
Seeber was surprised to find that the frequency used by the system is not one normally associated with public service or public infrastructure control. It is, instead, one that is close to those used by radio amateurs.
"I've demonstrated that even a $30 to $35 handheld radio you can buy from Amazon that is used by radio hobbyists — like a more enhanced walkie-talkie — is perfectly capable of perpetuating an attack when combined with a laptop," he says.
Once the frequency was known he began looking at the transmission itself and he soon found that the control signals were being sent with no encryption at all. That meant that anyone willing to put in the sort of effort he had made could analyze and hijack control of the system. Seeber then traveled to Sedgwick County, Kansas, where a similar system was in use, to see if the vulnerability also existed there. "The findings were consistent there and I did see the same pattern. And so I was able to confirm that their system was also vulnerable," he says.
While each system is customized to a great extent, Seeber says that an attacker could use their knowledge of the protocol to turn pre-programmed alerts on or off. In addition, he says that the system has a direct public-address mode, so it is possible that an attacker could use the infrastructure to broadcast an illicit message to the public over these public speakers.
At that point, Seeber and Bastille notified ATI, the system's vendor, of the SirenJack vuln. Seeber is eager to point out that the notification was in line with ethical analyst behavior. "We conducted this process with responsible disclosure," he says, adding, "That means that we write our findings up and and disclose it privately to the vendor, which we did in early January. Then we provide 90 days during which they're able to take those findings and prepare any remediation steps."
In a statement, ATI's CEO, Dr. Ray Bassiouni, said, "ATI is fully supportive of all of our clients and will be on standby if anyone is concerned about hacking or vulnerabilities in their system."
Seeber says that while Bastille was not asked to test the patch ATI provided to San Francisco, he has seen work on the pole-based components and has noticed random traffic within the signals, traffic that indicates at least some level of encryption is now in place.
"We don't want the public to lose confidence in the system and the government's ability to handle emergencies," Seeber says. He encourages more government agencies to test their emergency notification systems to avoid surprises in the future.
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