Ruby Deserialization Security: The Risk Hiding Inside Production Applications

By Naveed Ahmed | Lead DevOps & Platform Architect

A production service can appear completely healthy while still containing a serious security weakness.

The application responds to requests. Kubernetes reports healthy pods. Container scanning may show no known critical vulnerabilities.

But what if the application is reconstructing objects from data it doesn't fully trust?

That's the problem with unsafe deserialization.

Ruby's Marshal module is powerful, but it wasn't designed to safely reconstruct arbitrary objects from attacker-controlled input.

For engineering teams, this is a reminder that production security involves more than keeping runtime versions updated.

Why Deserialization Matters

Serialization converts data or objects into a format that can be stored or transferred.

Deserialization reconstructs that data.

Ruby provides native object serialization through Marshal.

The problem begins when untrusted input reaches a deserialization function that can recreate complex objects.

Depending on the application, unsafe object loading can expose dangerous behavior.

This is why Ruby's Marshal functionality should only be used with trusted serialized data.

For external data, simpler formats such as JSON are often more appropriate, together with strict validation.

Where Risk Can Enter an Application

Developers often focus on public API endpoints when reviewing security.

But serialized data can move through several parts of a system.

A background job might receive input from a queue. An application might retrieve serialized objects from a shared cache. A legacy integration might decode binary objects.

Each of these paths deserves review if the source of the data cannot be trusted.

This doesn't mean every background job or cache is insecure.

It means developers should understand the full data flow before assuming deserialization is safe.

Why Kubernetes Makes Investigation More Complicated

Imagine several Ruby applications running across multiple Kubernetes namespaces.

Some use different Ruby versions. Others have different dependencies. Several may share background processing infrastructure.

An engineer investigating potential security exposure first needs to know what's actually deployed.

For example:

kubectl get pods -A \
  -o custom-columns='NAMESPACE:.metadata.namespace,POD:.metadata.name,IMAGES:.spec.containers[*].image'

kubectl get pods -A \
  -o custom-columns='NAMESPACE:.metadata.namespace,POD:.metadata.name,IMAGES:.spec.containers[*].image'

Then check the Ruby runtime inside a candidate container:

kubectl exec -n production deploy/rails-api \
  -c web -- ruby -v

kubectl exec -n production deploy/rails-api \
  -c web -- ruby -v

These commands provide useful inventory information.

However, the presence of a particular Ruby version doesn't prove unsafe deserialization exists.

The investigation still needs application-level code review.

A Practical Production Security Approach

I'd focus on five things.

First, identify unsafe deserialization paths. Review how applications process serialized input, especially when that input comes from external or shared systems.

Second, maintain dependency visibility. Track Ruby versions, gems, operating system packages, and container images.

Third, use automated security scanning. Tools such as Trivy can identify known package vulnerabilities, while source analysis can help find risky application patterns.

Fourth, reduce unnecessary privileges. Containers and background workers should have only the access they need.

Finally, verify remediation in production. Updating a repository isn't the same as replacing every affected running image.

These practices help teams respond to both known vulnerabilities and application-level weaknesses.

The Bigger Lesson

One of the most important lessons in security engineering is that a clean vulnerability report doesn't necessarily mean an application is secure.

Automated scanners are excellent tools, but they cannot replace understanding how your software works.

Unsafe deserialization is a good example.

The weakness may be in the way an application processes data rather than in a specific outdated package.

That makes code review, runtime auditing, and least-privilege controls especially valuable.

Read the Complete Technical Guide

I've published a longer article covering Ruby2Shell claims, Ruby deserialization risks, Kubernetes auditing, container scanning, and production hardening.

Read the Ruby2Shell Security and Production Guide

The specific CVE-2026–113840 claims in that article are awaiting independent confirmation.

Final Thoughts

Security isn't just about fixing the latest CVE.

It's about knowing where your applications trust input, how data moves through your infrastructure, and whether your production controls actually reduce risk.

That's why unsafe deserialization deserves a place in every serious application security review.

How does your team find dangerous deserialization patterns in Ruby applications?

I'd be interested to hear what works in your environment.

Originally published on Naveed Ahmed's Engineering Blog.

Written by Naveed Ahmed — Lead DevOps & Platform Architect.

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