CVE-2026-54904 (High) detected in concurrent-ruby-1.3.6.gem

## CVE-2026-54904 - High Severity Vulnerability
Vulnerable Library - concurrent-ruby-1.3.6.gem

Modern concurrency tools including agents, futures, promises, thread pools, actors, supervisors, and more.
Inspired by Erlang, Clojure, Go, JavaScript, actors, and classic concurrency patterns.

Library home page: https://rubygems.org/gems/concurrent-ruby-1.3.6.gem

Path to dependency file: /Gemfile.lock

Path to vulnerable library: /vendor/cache/concurrent-ruby-1.3.6.gem

Dependency Hierarchy:
- activesupport-7.1.6.gem (Root Library)
- :x: **concurrent-ruby-1.3.6.gem** (Vulnerable Library)

Found in base branch: master

Vulnerability Details

concurrent-ruby is a modern concurrency tools for Ruby. Prior to 1.3.7, Concurrent::AtomicReference#update can enter a permanent busy retry loop when the current value is Float::NAN. The issue is caused by the interaction between AtomicReference#update, which retries until compare_and_set(old_value, new_value) succeeds; Numeric compare_and_set, which checks old == old_value before attempting the underlying atomic swap.; and Ruby NaN semantics, where Float::NAN == Float::NAN is always false. As a result, once an AtomicReference contains Float::NAN, calling #update repeatedly evaluates the caller's block and never returns. In services that store externally derived numeric values in an AtomicReference, this can cause CPU exhaustion or permanent request/job hangs. This vulnerability is fixed in 1.3.7.

Publish Date: 2026-06-24

URL: CVE-2026-54904

CVSS 3 Score Details (7.5)

Base Score Metrics:
- Exploitability Metrics:
- Attack Vector: Network
- Attack Complexity: Low
- Privileges Required: None
- User Interaction: None
- Scope: Unchanged
- Impact Metrics:
- Confidentiality Impact: None
- Integrity Impact: None
- Availability Impact: High

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Release Date: 2026-06-19

Fix Resolution: https://github.com/ruby-concurrency/concurrent-ruby.git - v1.3.7

***
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Start with /Gemfile.lock and /vendor/cache/concurrent-ruby-1.3.6.gem, then check how this repository manages Ruby dependencies. Upgrade concurrent-ruby to 1.3.7 and confirm the lockfile and vendored dependency no longer reference 1.3.6 or the reported vulnerable version.

Written by the indexing model from the issue text.