Ruby 4.0 Universal RCE Deserialization Gadget Chain | Hacker News Reader

Ruby 4.0 Universal RCE Deserialization Gadget Chain

elttam.com

78 pointspentestercrab22 comments

Doesn't this already require to be "on the other side of the airtight hatchway", or am I missing something?

The Marshal.load docs explicitly have a warning that you should not pass it untrusted data: https://docs.ruby-lang.org/en/master/Marshal.html#module-mar...

Yes, but that doesn't mean defense-in-depth isn't worth doing. The article discusses how known gadgets were removed in the past.

It's not a vulnerability, but it's an exploit. Most vulnerabilities in the wild never have an exploit written, because we mostly assume that for example arbitrary write or buffer overflow are dangerous and "can lead to arbitrary code execution", but actually exploiting them is hard.

This is someone who spend some time to write something to actually exploit sites with this vulnerability.

You only need one dev with the bright idea to pass data around via a clientside blob or cookie.

Which brings us to the old saying: Do not deserialize untrusted data.

In the context of Rubygems and their specs this obviously is harder to manage but dependencies such as Rubygems are and will always be part of your app's Trusted Computing Base.

> Do not deserialize untrusted data.

I think the better lesson is "use safe codecs"

> dependencies such as Rubygems are and will always be part of your app's Trusted Computing Base

This mindset is changing, in the npm ecosystem, managing and updating dependencies have become somewhat of a gamble. It is no longer if, its when you are compromised.

Gems/packages should explicitly declare what kind of features they need/want (file, net, deserialization, execute)

And when the sig. changes, you should get a warning

Very similar to the iOS entitlements

Checksumming the dependencies in the Gemfile may help. https://blog.rubygems.org/2024/12/19/bundler-v2-6.html

I have to use several gems that download and compile C sources from github at install time.

Accounts get compromised, no checksumming in the world can help with that.

Gemfile.lock checksums by default on bundler 4+

LLMs: hold my beer

Quoting the ruby documentation:

> Marshal.load is not suitable as a general purpose serialization format and you should never unmarshal user supplied input or other untrusted data.

I wrote one of the referenced posts describing the history here: https://blog.trailofbits.com/2025/08/20/marshal-madness-a-br...

I was also part of the team that audited RubyGems.org: https://github.com/trailofbits/publications/blob/master/revi...

Look at TOB-RGM-9 (an informational, largely out-of-scope finding) if you want to understand what could be done to mitigate some of these concerns. Nearly all of these gadget chains rely on Gem library functionality, which has this wonky .gemspec.rz metadata file that sits alongside the actual gem file. I understand that it'd be a challenging, backwards-incompatible change, but moving this file from Marshal to JSON would break a lot of these gadget chains. Perhaps there would be others, but it would raise the bar.

thanks for your work <3

That's actually crafty. I wonder what the rationale was for the C function time_mload(). Anyone able to find out? How can we see which person created it first?

The source code for that function is at https://github.com/ruby/ruby/blob/a75a8ccd9d2fa46eb68fe21469...

You can check the git blame and all the history. Unsurprisingly the function itself is from the 90s.

Did the OpenAI "sandbox" have Ruby available or a "sandboxed Ruby", which is an idiotic idea that would be fully expected from slop companies?

We are living in a post-fact society where we have to guess bits of information from YouTube videos and OpenAI slop statements. Maybe there should be a Senate hearing about the hack if that is what it takes.

I've yet to watch the BlackHat breakdown of how the "hack" (felony) proceeded, but being that it's OpenAI, it is safe to assume that the "sandbox" they speak of was a kitted-out Linux box with unmonitored network access.

The test environment was either intentionally setup to produce the outcome that it did or the sheer incompetence of a slop engineer was the catalyst for the crime. OpenAI is just an unscrupulous, childish company.

So much for coordinated disclosure, I guess.

the java ecosystem spent a decade on the same lesson. commons-collections was the first universal gadget library, and attempts to remove gadgets from the classpath were an endless game of catch-up. JEP 290 was the eventual solution: a filter mechanism that enforces which classes are even allowed to be deserialized, rather than trying to audit what classes exist. ruby doesn't have an equivalent. as long as marshal.load on untrusted input exists in the codebase, chasing individual gadgets isn't the fix.

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