Do you have to have matlab running on your rails server for this to happen?

▲ bradly an hour ago | parent | next [-]

Not running, but supported. You can check your app with:

    bin/rails runner '
      require "vips"
      puts "ruby-vips #{Vips::VERSION}  libvips #{Vips.version(0)}.#{Vips.version(1)}.#{Vips.version(2)}"
      begin
        Vips::Operation.new("matload")
        puts "matload PRESENT - this build can reach libmatio"
      rescue Vips::Error
        puts "matload ABSENT - this build cannot reach libmatio"
      end
    '

This is from the Rails official docs for the CVE which, interestingly, they only released as an agent skill. https://github.com/rails/rails-forensics-CVE-2026-66066/blob...

▲ fishtoaster an hour ago | parent | prev | next [-]

I think the answer is no - this would affect any Rails app with default settings that uses ActiveStorage. The "Preconditions" recap at the bottom here has all the appropriate caveats: https://ethiack.com/info-hub/research/kindarails2shell-how-a...

▲ rietta 2 hours ago | parent | prev [-]

I am not sure, but my read on the original disclosure is no. libvips itself has a variant processor for matlab v5 files, which the exploit took advantage of.

▲ kawsper 2 hours ago | parent [-]

libvips 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

	▲	rietta an hour ago \| parent [-]
		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.