The last several years have been fascinating for those of us who have been eagerly observing the steady move towards autonomous driving. While semi-autonomous vehicles have existed for many years, the vision of fleets of fully autonomous vehicles operating as a single connected entity is very much still a thing of the future. However, the latest technical advances in this area bring us a unique and compelling picture of some of the capabilities we might expect to see “down the road.” Pun intended.
For example, nearly every new vehicle produced in 2019 has a model which implements state-of-the art sensors that utilize analytics technologies, such as machine learning or artificial intelligence, and are designed to automate, assist or replace many of the functions humans were formerly responsible for. These can range from rain-sensors on the windshield to control wiper blades, to object detection sensors using radar and lidar for collision avoidance, to camera systems capable of recognizing objects in range and providing direct driving input to the vehicle.
This broad adoption represents a fascinating development in our industry; it’s one of those very rare times when researchers can lead the curve ahead of adversaries in identifying weaknesses in underlying systems.
McAfee Advanced Threat Research (ATR) has a specific goal: identify and illuminate a broad spectrum of threats in today’s complex landscape. With model hacking, the study of how adversaries could target and evade artificial intelligence, we have an incredible opportunity to influence the awareness, understanding and development of more secure technologies before they are implemented in a way that has real value to the adversary.
With this in mind, we decided to focus our efforts on the broadly deployed MobilEye camera system, today utilized across over 40 million vehicles, including Tesla models that implement Hardware Pack 1.
18 Months of Research
McAfee Advanced Threat Research follows a responsible disclosure policy, as stated on our website. As such, we disclosed the findings below to both Tesla and MobilEye 90 days prior to public disclosure. McAfee disclosed the findings to Tesla on September 27th, 2019 and MobilEye on October 3rd, 2019. Both vendors indicated interest and were grateful for the research but have not expressed any current plans to address the issue on the existing platform. MobilEye did indicate that the more recent version(s) of the camera system address these use cases.
MobilEye is one of the leading vendors of Advanced Driver Assist Systems (ADAS) catering to some of the world’s most advanced automotive companies. Tesla, on the other hand, is a name synonymous with ground-breaking innovation, providing the world with the innovative and eco-friendly smart cars.
Tesla models used to conduct our experiments on. Left: Tesla model X (2016) Right: Tesla model S (2016)
A table showing MobilEye’s EyeQ3 being used in Tesla’s hardware pack 1. Source: Wikipedia, MobilEye
As we briefly mention above, McAfee Advanced Threat Research has been studying what we call “Model Hacking,” also known in the industry as adversarial machine learning. Model Hacking is the concept of exploiting weaknesses universally present in machine learning algorithms to achieve adverse results. We do this to identify the upcoming problems in an industry that is evolving technology at a pace that security has not kept up with. We started our journey into the world of model hacking by replicating industrypapers on methods of attacking machine learning image classifier systems used in autonomous vehicles, with a focus on causing misclassifications of traffic signs. We were able to replicate and significantly expand upon previous research focused on stop signs, including both targeted attacks, which aim for a specific misclassification, as well as untargeted attacks, which don’t prescribe what an image is misclassified as, just that it is misclassified. Ultimately, we were successful in creating extremely efficient digital attacks which could cause misclassifications of a highly robust classifier, built to determine with high precision and accuracy what it is looking at, approaching 100% confidence.
Targeted digital white-box attack on stop sign, causing custom traffic sign classifier to misclassify as 35-mph speed sign
We further expanded our efforts to create physical stickers, shown below, that model the same type of perturbations, or digital changes to the original photo, which trigger weaknesses in the classifier and cause it to misclassify the target image.
Targeted physical white-box attack on stop sign, causing custom traffic sign classifier to misclassify the stop sign as an added lane sign
This set of stickers has been specifically created with the right combination of color, size and location on the target sign to cause a robust webcam-based image classifier to think it is looking at an “Added Lane” sign instead of a stop sign.
Video demo of our resilient classifier in the lab which correctly recognizes the 35-mph speed limit sign, even when it is partially obstructed
In reality, modern vehicles don’t yet rely on stop signs to enable any kind of autonomous features such as applying the brakes, so we decided to alter our approach and shift (pun intended) over to speed limit signs. We knew, for example, that the MobilEye camera is used by some vehicles to determine the speed limit, display it on the heads-up display (HUD), and potentially even feed that speed limit to certain features of the car related to autonomous driving. We’ll come back to that!
We then repeated the stop sign experiments on traffic signs, using a highly robust classifier, and our trusty high-resolution webcam. And just to show how robust our classifier is, we can make many changes to the sign— block it partially, place the stickers in random locations — and the classifier does an outstanding job of correctly predicting the true sign, as demonstrated in the video above. While there were many obstacles to achieving the same success, we were ultimately able to prove both targeted and untargeted attacks, digitally and physically, against speed limit signs. The below images highlight a few of those tests.
Example of our resilient classifier correctly classifying the 35-mph speed sign with 95.93% confidence
Example of targeted digital perturbations printed out using a black and white printer which cause a misclassification of 35-mph speed sign to 45-mph speed sign.
Physical targeted black-box attack on speed limit 35 sign resulting in a misclassification of the sign to a 45-mph sign
Black-box attack on the 35-mph sign, resulting in a misclassification of 45-mph sign. This attack also transfers on state-of-the-art CNNs namely Inception-V3, VGG-19 and ResNet-50
At this point, you might be wondering “what’s so special about tricking a webcam into misclassifying a speed limit sign, outside of just the cool factor?” Not much, really. We felt the same, and decided it was time to test the “black box theory.”
What this means, in its most simple form, is attacks leveraging model hacking which are trained and executed against white box, also known as open source systems, will successfully transfer to black box, or fully closed and proprietary systems, so long as the features and properties of the attack are similar enough. For example, if one system is relying on the specific numeric values of the pixels of an image to classify it, the attack should replicate on another camera system that relies on pixel-based features as well.
The last part of our lab-based testing involved simplifying this attack and applying it to a real-world target. We wondered if the MobilEye camera was as robust as the webcam-based classifier we built in the lab? Would it truly require several highly specific, and easily noticeable stickers to cause a misclassification? Thanks to several friendly office employees, we were able to run repeated tests on a 2016 Model “S” and 2016 Model “X” Tesla using the MobilEye camera (Tesla’s hardware pack 1 with EyeQ3 mobilEye chip). The first test involved simply attempting to recreate the physical sticker test – and, it worked, almost immediately and with a high rate of reproducibility.
These adversarial stickers cause the MobilEye on Tesla Model X to interpret the 35-mph speed sign as an 85-mph speed sign
In our lab tests, we had developed attacks that were resistant to change in angle, lighting and even reflectivity, knowing this would emulate real-world conditions. While these weren’t perfect, our results were relatively consistent in getting the MobilEye camera to think it was looking at a different speed limit sign than it was. The next step in our testing was to reduce the number of stickers to determine at which point they failed to cause a misclassification. As we began, we realized that the HUD continued to misclassify the speed limit sign. We continued reducing stickers from 4 adversarial stickers in the only locations possible to confuse our webcam, all the way down to a single piece of black electrical tape, approximately 2 inches long, and extending the middle of the 3 on the traffic sign.
A robust, inconspicuous black sticker achieves a misclassification from the Tesla model S, used for Speed Assist when activating TACC (Traffic Aware Cruise Control)
Even to a trained eye, this hardly looks suspicious or malicious, and many who saw it didn’t realize the sign had been altered at all. This tiny piece of sticker was all it took to make the MobilEye camera’s top prediction for the sign to be 85 mph.
Black tape attack shows the 35-mph sign being incorrectly read as an 85-mph sign on the HUD of a Tesla model X
The finish line was close (last pun…probably).Finally, we began to investigate whether any of the features of the camera sensor might directly affect any of the mechanical, and even more relevant, autonomous features of the car. After extensive study, we came across a forum referencing the fact that a feature known as Tesla Automatic Cruise Control (TACC) could use speed limit signs as input to set the vehicle speed.
There was majority of consensus among owners that this might be a supported feature. It was clear that there was also confusion among forum members as to whether this capability was possible, so our next step was to verify by consulting Tesla software updates and new feature releases.
A software release for TACC contained just enough information to point us towards speed assist, with the following statement, under the Tesla Automatic Cruise Control feature description.
“You can now immediately adjust your set speed to the speed determined by Speed Assist.”
This took us down our final documentation-searching rabbit hole; Speed Assist, a feature quietly rolled out by Tesla in 2014.
Finally! We can now add these all up to surmise that it might be possible, for Tesla models enabled with Speed Assist (SA) and Tesla Automatic Cruise Control (TACC), to use our simple modification to a traffic sign to cause the car to increase speed on its own!
Despite being confident this was theoretically possible, we decided to simply run some tests to see for ourselves.
McAfee ATR’s lead researcher on the project, Shivangee Trivedi, partnered with another of our vulnerability researchers Mark Bereza, who just so happened to own a Tesla that exhibited all these features. Thanks Mark!
For an exhaustive look at the number of tests, conditions, and equipment used to replicate and verify misclassification on this target, we have published our test matrix here.
The ultimate finding here is that we were able to achieve the original goal. By making a tiny sticker-based modification to our speed limit sign, we were able to cause a targeted misclassification of the MobilEye camera on a Tesla and use it to cause the vehicle to autonomously speed up to 85 mph when reading a 35-mph sign. For safety reasons, the video demonstration shows the speed start to spike and TACC accelerate on its way to 85, but given our test conditions, we apply the brakes well before it reaches target speed. It is worth noting that this is seemingly only possible on the first implementation of TACC when the driver double taps the lever, engaging TACC. If the misclassification is successful, the autopilot engages 100% of the time. This quick demo video shows all these concepts coming together.
Of note is that all these findings were tested against earlier versions (Tesla hardware pack 1, mobilEye version EyeQ3) of the MobilEye camera platform. We did get access to a 2020 vehicle implementing the latest version of the MobilEye camera and were pleased to see it did not appear to be susceptible to this attack vector or misclassification, though our testing was very limited. We’re thrilled to see that MobilEye appears to have embraced the community of researchers working to solve this issue and are working to improve the resilience of their product. Still, it will be quite some time before the latest MobilEye camera platform is widely deployed. The vulnerable version of the camera continues to account for a sizeable installation base among Tesla vehicles. The newest models of Tesla vehicles do not implement MobilEye technology any longer, and do not currently appear to support traffic sign recognition at all.
Looking Forward
We feel it is important to close this blog with a reality check. Is there a feasible scenario where an adversary could leverage this type of an attack to cause harm? Yes, but in reality, this work is highly academic at this time. Still, it represents some of the most important work we as an industry can focus on to get ahead of the problem. If vendors and researchers can work together to identify and solve these problems in advance, it would truly be an incredible win for us all. We’ll leave you with this:In order to drive success in this key industry and shift the perception that machine learning systems are secure, we need to accelerate discussions and awareness of the problems and steer the direction and development of next-generation technologies. Puns intended.
