CVE-2026-25794: ImageMagick has heap-buffer-overflow via signed integer overflow in WriteUHDRImage when writing UHDR images with large dimensions

WriteUHDRImage in coders/uhdr.c uses int arithmetic to compute the pixel buffer size. When image dimensions are large, the multiplication overflows 32-bit int, causing an undersized heap allocation followed by an out-of-bounds write. This can crash the process or potentially lead to an out of bounds heap write.

==1575126==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7fc382ef3820 at pc 0x5560d31f229f bp 0x7ffe865f9530 sp 0x7ffe865f9520
WRITE of size 8 at 0x7fc382ef3820 thread T0