alt Hacker Newslibvips also have a block_untrusted mode where it will block unsafe loaders, .mat seems to be marked as untrusted:
vips -l
VipsForeignLoadMat (matload), load mat from file (.mat), priority=0, untrusted, is_a, get_flags, get_flags_filename, header, load
Correct, which is how the ActiveStorage gem was patched. After this, Rails raises a Vips::Error: VipsForeignLoad exception on an attempted variant render of a malicious file. I plan on writing a technical detail post soon with some more code level details and "indicators of compromise" but this one was getting long. This is more for management to understand why wait to patch is a major issue. The discovery to active exploit attempt timeline is the story here.