[delayed]
Just sent this to my boss. Felt like tossing a grenade over a fence into a party of unsuspecting people.
We don’t use ActiveStorage but Claude was able create a similar exploit in own our app in the exact same way via our own file upload library in 3 minutes simply by point Opus 5 at our site and asking it if we were vulnerable to an attack similar to KindaRails2Shell.
What a time to be alive.
Nice write up, Claude.
Do you have to have matlab running on your rails server for this to happen?
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
'
Why would you have matlab on an external server? People don't even have a compiler on the server in this situation. Crazy.
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...
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.
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, loadCorrect, 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.
i thought cloudflare would protect against those no?
Cloudflare or a WAF may or may not help. These can often catch and block specific bot traffic, but not every attack payload is delivered naively. It would be part of a defense in depth. Having the underlying vulnerability fixed is critically important. For those on AWS, WAF & Shield is also very useful but at the end of the day these let legitimate traffic through, such as legitimately uploading a file that only in its contents is malformed.
Where does it say the site used Cloudflare?
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DHH needs to focus on Rails again rather than Omarchy.
He’s still very supportive of Rails. Come join us at RailsWorld in Austin later this month and see for yourself!
What does DHH have to do with this? Omarchy itself isn’t known for being secure; here is a root escalation from five days ago https://news.ycombinator.com/item?id=49499854
The rails developers are incredibly smart and capable. They patched the exploit. The problem is that it’s too easy to reverse engineer based on the patch. They can’t do anything about that.
> What does DHH have to do with this?
DHH created Rails.
He's also a Nazi
This post could be 10% as long:
- There was a bug with a patch
- We applied it to our clients
- There were live exploits within eight hours of the patch being released
- The Rails team had to expedite release of the technical details because POCs obviated the need to embargo