Ruby Regexp RCE Fixes: What Rails App Owners Should Check

• What Ruby announced
• Start with the feature, then trace the input
• When users want text search, preserve text semantics
• My upgrade from Ruby 3.4.9 to 3.4.12 hit an ffi build failure
• Ship the runtime update through the whole application
• Give the application owner a useful answer

A security release lands, and someone asks: “Is our Rails application affected?”

I want that answer to come with evidence: which feature accepts the relevant input, which runtime is deployed, and what has actually changed in production. A merged version update is only one part of that answer.

Ruby’s October 23, 2026 regexp fixes are a good reason to ask those questions now. Here is the upstream finding, followed by the review and release approach I recommend for an existing Rails product.

What Ruby announced

The Ruby announcement describes memory-corruption bugs during regexp compilation. GitLab demonstrated remote code execution through attacker-supplied patterns. Ruby recommends these releases or later:

Ruby 4.0.8 lacks one fix. The affected boundary is compiling attacker-controlled patterns through APIs such as Regexp.new, Regexp.compile, or interpolation. Developer-authored fixed expressions are outside the advisory’s scope. Regexp.timeout and pattern-length limits do not reliably prevent these compilation bugs.

The identifiers belong to GitLab: CVE-2026-89078, CVE-2026-93577, CVE-2026-97229, and CVE-2026-110264. At publication, Ruby had not requested separate identifiers. The announcement also names Regexp.union; review its argument types rather than treating every call as equivalent.

If an immediate upgrade is impossible, upstream recommends stopping compilation of untrusted patterns. Recheck the announcement for updates when acting on this article.

Start with the feature, then trace the input

My first review question would be: can a customer or another external system supply a pattern, or only the text being searched?

For example, these two operations have different purposes:

# The developer defines the pattern; the user supplies text to match.
/\A[A-Z]{2}\z/.match?(submitted_country_code)

# Review this boundary: the user supplies the pattern itself.
Regexp.new(submitted_pattern).match?(document_text)

These are illustrative examples, not exploit payloads. The second operation might sit behind a saved search, an import rule, or a tenant’s configurable filter. Those are places I would investigate, not claims that every such feature is vulnerable.

Do not stop at the controller. A pattern could be stored in a database today and compiled by a background job tomorrow. An admin screen also deserves review: record who can change the value and which systems can populate it.

As a starting inventory, search the application and supporting scripts:

rg -n 'Regexp\.(new|compile|union)' app lib config
rg -n -F '#{' app lib config

The second search deliberately returns unrelated interpolation too. Inspect regexp literals, including %r{...}, among the results. These commands are leads for review; wrappers, dependencies, and indirect calls need separate inspection.

For each relevant call, record the input’s origin, who controls it, whether it is escaped, and where compilation runs. That makes the finding actionable for the person responsible for the release.

When users want text search, preserve text semantics

Before retaining a configurable regexp, ask what the feature needs to do. If it only needs a literal substring check, a string operation may be enough:

document_text.include?(search_text)

This example is case-sensitive. It changes behavior if users previously relied on regexp syntax, so agree the intended behavior before replacing production code.

If a fixed expression needs an embedded literal value, Ruby documents Regexp.escape for escaping metacharacters:

pattern = Regexp.new(Regexp.escape(search_text), Regexp::IGNORECASE)
pattern.match?(document_text)

Keep the escaping immediately next to construction and test the intended search behavior. For example, a.b should find a literal dot if the product promises text search. Check empty values, case handling, and encoding expectations as relevant to your data.

I would treat this as a product and code review alongside the runtime update. I would not assume that accepting arbitrary pattern syntax becomes a sensible feature simply because a patch is available.

My upgrade from Ruby 3.4.9 to 3.4.12 hit an ffi build failure

When I tried this upgrade myself, moving from Ruby 3.4.9 to 3.4.12, bundle install failed while building ffi 1.16.3 on my Apple Silicon Mac. In this application, the dependency came through flat-ui-sass, bootstrap-sass, and sassc.

The build log showed the bundled libffi being compiled, then stopped with:

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
error: invalid CFI advance_loc expression
An error occurred while installing ffi (1.16.3), and Bundler cannot continue.

The blocker was compiling ffi’s bundled libffi with my Xcode tools. I fixed it by telling ffi to use Homebrew’s libffi instead:

brew install libffi
bundle config set --local build.ffi "--enable-system-libffi --with-ffi-dir=$(brew --prefix libffi)"
bundle install

Homebrew’s libffi was already installed on my machine, so I only needed the last two commands. Using brew --prefix libffi avoided hard-coding the Homebrew installation path. The Bundler setting applies locally to this project; it describes how to build ffi on this machine, rather than a deployment setting for every environment.

I also updated the RUBY VERSION entry in Gemfile.lock from ruby 3.4.9p82 to ruby 3.4.12p148 to match the runtime upgrade. That metadata change records the version; it does not install Ruby or replace running processes.

This resolved my local installation blocker. It is one concrete example of why I leave room for native dependency checks even in a patch-level security update. A build failure on my development machine does not establish that Ruby 3.4.12 is broken generally, and getting Bundler working locally is still only a step toward the production verification below.

Ship the runtime update through the whole application

My recommended release checklist is:

1. Inventory what runs. Record Ruby versions for web processes, workers, scheduled jobs, and separately built services. Capture RUBY_DESCRIPTION from each environment’s execution context. A fresh console alone does not prove every long-running process has been replaced.
2. Align the version declarations. Check .ruby-version, the Gemfile’s Ruby declaration, lockfile metadata, Docker base images, CI configuration, and hosting settings where applicable. Use the patched release appropriate to the application’s series; avoid introducing a major-version migration into a focused patch without a reason.
3. Build and verify. Rebuild the application artifact, run the relevant regression checks, and exercise search, imports, rules, and jobs that the review identified. Do not try malicious patterns against production as a verification shortcut.
4. Deploy every process type. Replace web and worker processes and update scheduled execution environments. Check for old instances left behind after a partial rollout.
5. Record completion. Keep the deployed artifact identifier, runtime evidence, workflow checks, and any temporarily disabled functionality with the release record.

Agree recovery before deployment. If rollback restores the previous runtime, it can also restore the exposure; decide how the affected feature will remain unavailable while a release problem is resolved.

For applications on an older Ruby series, scope a compatible path to a supported runtime. Our upgrade planning guide explains how I would separate compatibility investigation from implementation.

Give the application owner a useful answer

I would report the result in four lines: the input path reviewed, the deployed runtime, the checks completed, and any unresolved work. If exposure is still uncertain, name the missing evidence and the person responsible for resolving it.

At WideFix, we take technical ownership of existing Rails applications and provide ongoing maintenance. Security updates belong in that responsibility: someone needs to connect the advisory to the application’s behavior and follow the change into production.

If your original developer has left, our Rails application takeover service provides a starting point for understanding the codebase and its deployment. Bring your known Ruby version and any configurable search or matching features. The useful next step is to agree the review scope, identify the running environments, and plan the first verified release.

Published October 26, 2026. Version recommendations above reflect the linked October 23 releases; check current upstream guidance before upgrading.