  Depth estimation-based obstacle avoidance has been widely adopted by
autonomous systems (drones and vehicles) for safety purpose. It normally relies
on a stereo camera to automatically detect obstacles and make flying/driving
decisions, e.g., stopping several meters ahead of the obstacle in the path or
moving away from the detected obstacle. In this paper, we explore new security
risks associated with the stereo vision-based depth estimation algorithms used
for obstacle avoidance. By exploiting the weaknesses of the stereo matching in
depth estimation algorithms and the lens flare effect in optical imaging, we
propose DoubleStar, a long-range attack that injects fake obstacle depth by
projecting pure light from two complementary light sources.
  DoubleStar includes two distinctive attack formats: beams attack and orbs
attack, which leverage projected light beams and lens flare orbs respectively
to cause false depth perception. We successfully attack two commercial stereo
cameras designed for autonomous systems (ZED and Intel RealSense). The
visualization of fake depth perceived by the stereo cameras illustrates the
false stereo matching induced by DoubleStar. We further use Ardupilot to
simulate the attack and demonstrate its impact on drones. To validate the
attack on real systems, we perform a real-world attack towards a commercial
drone equipped with state-of-the-art obstacle avoidance algorithms. Our attack
can continuously bring a flying drone to a sudden stop or drift it away across
a long distance under various lighting conditions, even bypassing sensor fusion
mechanisms. Specifically, our experimental results show that DoubleStar creates
fake depth up to 15 meters in distance at night and up to 8 meters during the
daytime. To mitigate this newly discovered threat, we provide discussions on
potential countermeasures to defend against DoubleStar.
