A flaw was found in GIMP’s X cursor (XMC) thumbnail loader. When GIMP generates a thumbnail for a crafted XMC file, it allocates a pixel buffer using a width * height size computed in 32-bit signed arithmetic. If that product overflows, the allocation is smaller than the true image extent. A subsequent GEGL buffer read uses the unwrapped dimensions and performs an out-of-bounds read on the heap (CWE-125), after integer overflow in the size calculation (CWE-190). This can crash GIMP or corrupt process memory.
To mitigate only open X cursor and other image files from trusted sources; do not preview untrusted files in GIMP.