Blender before 4.5.15 and 5.x before 5.2.3 contains a heap buffer overflow vulnerability in the blend file thumbnail extractor caused by 32-bit integer overflow in thumb_data_vertical_flip(). Attackers can craft a .blend file with malicious TEST block dimensions that trigger an out-of-bounds write when blender-thumbnailer or the Windows shell extension previews it, causing crashes or code execution.