6 ms·

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

rietta 12d ago
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 12d ago
  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 12d ago
    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.
bradly 12d ago
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/main/skills/kr2s-was-i-vulnerable/references/guide.md https://github.com/rails/rails-forensics-CVE-2026-66066/blob...
- comrade1234 12d ago
  Why would you have matlab on an external server? People don't even have a compiler on the server in this situation. Crazy.
- XenoCyber0 12d ago
  An agent skill is the official distribution format for the forensics on a 9.5. I mean, I get it, anyone running a Rails app right now is pasting "am I affected" into an agent anyway, but it's the kind of thing that would've sounded like a joke a couple years ago.
  - TeMPOraL 11d ago
    Makes sense though. Agent skills are - by a mix of LLM nature and fashion - just high-quality documentation. Documentation that only gets written now, because agents are what makes docs "something immediately and directly useful for me right now", vs. "something I should write so others may benefit, someday, somehow". Human incentives are funny.
    - XenoCyber0 8d ago
      [dead]
fishtoaster 12d ago
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-matlab-file-reads-your-secrets-and-pops-a-shell-on-ruby-on-rails https://ethiack.com/info-hub/research/kindarails2shell-how-a...

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 12d ago
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 12d ago
  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.

bradly 12d ago

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/main/skills/kr2s-was-i-vulnerable/references/guide.md https://github.com/rails/rails-forensics-CVE-2026-66066/blob...

comrade1234 12d ago
Why would you have matlab on an external server? People don't even have a compiler on the server in this situation. Crazy.
XenoCyber0 12d ago
An agent skill is the official distribution format for the forensics on a 9.5. I mean, I get it, anyone running a Rails app right now is pasting "am I affected" into an agent anyway, but it's the kind of thing that would've sounded like a joke a couple years ago.
- TeMPOraL 11d ago
  Makes sense though. Agent skills are - by a mix of LLM nature and fashion - just high-quality documentation. Documentation that only gets written now, because agents are what makes docs "something immediately and directly useful for me right now", vs. "something I should write so others may benefit, someday, somehow". Human incentives are funny.
  - XenoCyber0 8d ago
    [dead]

fishtoaster 12d ago

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-matlab-file-reads-your-secrets-and-pops-a-shell-on-ruby-on-rails https://ethiack.com/info-hub/research/kindarails2shell-how-a...