Research team outline a traffic light hack that could bring down a city


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Prof Bill Buchanan has outlined the methods used in a recent traffic light hack, and which could bring down the traffic infrastructure within a city (The Conversation) and (Blog).

The research team are currently submitting for an EU Project in critical infrastructure protection, and aim to use their knowledge to protect critical infrastructure in Europe.


As we move into an Information Age we becoming increasing dependent on data for the control of our infrastructures, which leaves them open to attackers. Often critical infrastructure is obvious, such as the energy supplies for data centers, but it is often the ones which are the least obvious that are the most open to attack. This could be for an air conditioning system in a data centre, where a failure can cause the equipment to virtually melt (especially tape drives) or in the control of traffic around a city. As we move towards using data to control and optimize our lives we become more dependence on it.

Traffic Light Hacking

So, to prove a point, security researchers, lead by Alex Halderman at the University of Michigan, managed to use a laptop and an off-the-shelf radio transmitter to control traffic light signals ( Overall they found many security vulnerabilities and managed to control over 100 traffic signals within Michigan City using a single laptop. In order to be ethical in their approach the gained full permission form the road agency, and made sure that there was no danger to drivers. Their sole motivation was to show that traffic control infrastructure could be easily taken over.

Overall they found a weak implementation of security with the usage of open and unencrypted radio signals, which allowed intruders to tap into their communications, and then discovered the usage of factory-default usernames and passwords. Along with this there was a debugging port which could be easily compromised.

In the US, the radio frequency used to control traffic lights is typically in the ISM band at 900 MHz or 5.8 GHz, which makes it fairly easy to get equipment to communicate with the radio system. The researchers used readily available wireless equipment and single laptop to read the unencrypted data on the wireless network.

Figure 1 provides an overview of the control system where the radio transmits a live feed (and other sensed information) to the road agency. The MMU (Malfunction Management Unit) is the failsafe operator on the system and ensures that the lights are not put into an unsafe state (such as for Red and Green at the same time), and the lights are then adjusted using the information gained from the induction loops in the road (and which senses cars as they pass over it). If control can be gained to the MMU, and allow for access to the controller, the lights can be compromised to go into incorrect states, or to stay at steady red (and cause a grid lock within a city). Within the MMU controller board, the researchers found that by connecting a jumper wire, the output from the controller was ignored, and the intersection put into a known-safe state.


Figure 1: Overview of traffic control system

Small old debug port

A typical security problem in many control systems is that there is often a debug port, which gives highly priviledged access to the system. Within this compromise, the researchers found that the control boxes ran VxWorks 5.5, which leaves a debug port open for testing. They then sniffed the packages between the controller and the MMU, and found that there was no authentication used, and that the messages were not encrypted and can be easily viewed and replayed. This allowed them to reverse engineer the messaging protocol for the lights. They then created a program to activate any of the buttons witin the controller and display the results, and then even to access the controller remotely. In the end they managed to turn all the lights in the neighournood to red (or all green on a given route – in order to operate safely within the experiment).


Finally they found that the units were suspectiable to a denial-of-service (DoS) attack, where continual accesses with incorrect control signals over the network caused the malfunction management unit to put the lights in a failure state (all red).



This vulnerability showed all the standard signs of the bad integration of security, and which is common in many systems, where security is not thought of as a major concern. This is not a small scale issue, as the researchers identified that this type of system is used in more than 60% of the traffic intersections in the US. If a malicious agent wanted to bring a city, or even a country to its knees, they could just flip a switch … and there is no road transport system, which can then cause chaos to the rest of the infrastructure. We really need to think the way that systems are designed, and probe them for their vulnerabilties.

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Associated people

William Buchanan
Director of CDCS
+44 131 455 2759
Bruce Ramsay
Senior Research Fellow
+44 131 455 2746
Electronic information now plays a vital role in almost every aspect of our daily lives. So the need for a secure and trustworthy online infrastructure is more important than ever. without it, not only the growth of the internet but our personal interactions and the economy itself could be at risk.