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Analyzing the Security of Traffic Infrastructure

WC 567 / RT 3min

Green Lights Forever

Safety critical nature of traffic infrastructure requires that it be secure against computer-based attacks.

Traffic signals were originally designed as standalone hardware, each running on fixed timing schedules, but have evolved into more complex, networked systems.

Traffic controllers now store multiple timing plans, integrate varied sensor data, and even communicate with other intersections in order to better coordinate traffic.

Wireless networking has helped to mitigate these costs, and many areas now use intelligent wireless traffic management systems.


Traffic controllers read sensor inputs and control light states. The controller is typically placed in a metal cabinet by the roadside along with relays to activate the traffic lights.


Radios commonly operate in the ISM band at 900 MHz or 5.8 GHz, or in the 4.9 GHz band allocated for public safety.


Malfunction management unit, also referred to as conflict management units, are hardware-level safety mechanisms

Valid configurations are stored on a circuit board rather than in software, with safe configurations literally wired together.

If an unsafe configuration (e.g. conflicting green lights) is detected, the MMU overrides the controller and forces the lights into a known-safe configuration.

The MMU also ensures that durations of lights are long enough. Too short of a yellow or red light duration will trigger a fault.


One intersection acts as a root node and connects back to a management server under the control of the road agency. Intersections often have two radios, one slave radio to transmit to the next intersection towards the root and one master radio to receive from one or more child nodes beyond it. All devices form a single private network and belong to the same IP subnet.

The proprietary protocol is similar to 802.11 and broadcasts an SSID which is visible from standard laptops and smartphones but cannot be connected to.

The wireless connections are unencrypted and the radios use factory default usernames and passwords.


A single controller at each intersection reads sensor data and controls the traffic lights and pedestrian signs. Many settings on the controller are programmable, including light timing parameters.

All of the settings on the controller may be configured via the physical interface on the controller, but they may also be modified though the network. An FTP connection to the device allows access to a writable configuration database. This requires a username and password, but they are fixed to default values which are published online by the manufacturer. It is not possible for a user to modify the FTP username or password.

The controller runs the VxWorks 5.5 real-time operating system.


Types of attacks

DOS - A denial of service attack in this context refers to stopping normal light functionality. The most obvious way to cause a loss of service is to set all lights to red.

Traffic Congestion - more subtly, attacks could be made against the entire traffic infrastructure of a city which would manipulate the timings of an intersection relative to its neighbors.

Light Control - An attacker can also control lights for personal gain. Lights could be changed to be green along the route the attacker is driving.


MMU - Malfunction management unit

Denial of service