CVE-2026-54906 (Medium) detected in concurrent-ruby-1.3.6.gem

## CVE-2026-54906 - Medium 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::ReadWriteLock#release_write_lock does not verify that the calling thread acquired the write lock. Any thread with access to the lock object can release an active write lock held by another thread. A second writer can then enter its critical section while the first writer is still running. Concurrent::ReadWriteLock#release_read_lock also decrements the shared counter even when no read lock is held. Calling it on a fresh lock changes the counter from 0 to -1, after which normal read acquisition raises Concurrent::ResourceLimitError. This is a synchronization correctness issue in the public Concurrent::ReadWriteLock API. This vulnerability is fixed in 1.3.7.

Publish Date: 2026-06-24

URL: CVE-2026-54906

CVSS 3 Score Details (4.0)

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

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 the cached dependency at vendor/cache/concurrent-ruby-1.3.6.gem, then review the CVE details and suggested fix. Upgrade concurrent-ruby to 1.3.7 and update the dependency references; done means the vulnerable 1.3.6 version is no longer present.

Written by the indexing model from the issue text.