CVE-2026-1837 libjxl: Out-of-bounds write in grayscale color transformation when using LCMS2

A specially-crafted file can cause libjxl's decoder to write pixel data to uninitialized unallocated memory. Soon after that data from another uninitialized unallocated region is copied to pixel data. This can be done by requesting color transformation of grayscale images to another grayscale col...