UBUNTU-CVE-2026-70654: Medium severity ubuntu/vips vulnerability

libvips is a fast image processing library with low memory needs. Prior to version 8.18.3, applications that define unusual custom libvips sources and use them to process untrusted uncompressed PPM images can trigger a max/min error in vipssourcereadtomemory in libvips/iofuncs/source.c. The function uses VIPSMAX instead of VIPSMIN when selecting the remaining read size, allowing up to 4032 bytes to be written beyond the allocated heap buffer and causing memory corruption or a process crash. This issue is fixed in version 8.18.3.