What exactly caused the Dallas siren hack?

Two Fridays ago around midnight, an individual hacked and triggered the emergency siren system used in Dallas to warn for tornadoes and other emergencies. That same person kept the alarms going for 95 minutes even after emergency service workers shut them off. The full system had to be shut down.

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Initially, Dallas officials blamed a “hack” for causing every tornado siren to go off at midnight and interpreted a network intrusion into Dallas’ emergency services computer systems. However, in the most recent statement, Dallas City Manager, T.C. Broadnax, clarified that the cause of the “hack” was a radio signal that tricked the system to gain control of the siren network.

“I don’t want someone to understand how it was done so that they could try to do it again,” Broadnax said. “It was not a system software issue; it was a radio issue.”

Measures were taken to prevent the incident from occurring again, but again, Broadnax would not go into detail.

Older alert sirens like the ones used in Dallas are typically controlled by tone combinations utilized by the Emergency Alert System and broadcast over the National Weather Service’s weather radio. They can also be controlled via Dual-Tone Multi-Frequency (DTMF) or Audio Frequency Shift Keying (AFSK) coded commands from either a center or dispatcher and sent over UHF radio frequencies.

It’s possible that the frequency used by the sirens for DTMF or AKSK wasn’t monitored, allowing an attacker to broadcast an infinite number of guesses at the ended commands until the sirens were off. They would then just have to simply repeat the command signal. However, it’s also possible that someone gained access to documentation for the siren system and knew which commands to send.

Regardless of how it was done, the Dallas siren hack has spurred extra attention in other areas. Officials in Edmond, Oklahoma, are preparing themselves to update their systems frequently and are confident that they will be able to deal with a similar threat if need be. The city of Denison in Texas is also updating and replacing their severe weather emergency sirens over the next few months.

Source: Ars Technica