An out-of-bounds read was discovered in OpenCV before 4.1.1 (OpenCV-Python before 4.1.0.25). Specifically, variable coarsest scale is assumed to be greater than or equal to finest scale within the calc()/ocl calc() functions in dis flow.cpp. However, this is not true when dealing with small images, leading to an out-of-bounds read of the heap-allocated arrays Ux and Uy.