OpenSlide is a C library for reading whole slide image files. From 3.4.1 until 4.0.1, OpenSlide's parse_level0_xml() processing in src/openslide-vendor-ventana.c accepts nonpositive row or column tile counts from a crafted Ventana BIF file. The invalid counts produce attacker-controlled relative memory offsets and allow arbitrary values to be written at those offsets, affecting all supported platforms and configurations and resulting in a crash or potential arbitrary code execution. This issue is fixed in version 4.0.1.