CVE-2026-54905 (Medium) detected in concurrent-ruby-1.3.6.gem

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Quiet
Tech stack
ruby
Domain
security

Research direction

Start with /Gemfile.lock and the cached dependency at /vendor/cache/concurrent-ruby-1.3.6.gem, then review the dependency hierarchy in the issue. Update the concurrent-ruby dependency to 1.3.7 and verify that the lockfile and cached gem no longer contain the vulnerable version.

Written by the indexing model from the issue text.

Description

Mend: dependency security vulnerability

CVE-2026-54905 - 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:

  • manageiq-style-1.6.1.gem (Root Library)
    • rubocop-rails-2.34.3.gem
      • activesupport-8.0.5.gem
        • ❌ 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::ReentrantReadWriteLock can incorrectly grant a write lock after one thread acquires the read lock 32,768 times. The lock stores a thread's local read and write hold counts in one integer. The low 15 bits are used for the read hold count, and bit 15 is used as WRITE_LOCK_HELD. After 32,768 reentrant read acquisitions, the local read count crosses into the write-lock bit. try_write_lock then treats the thread as already holding a write lock and returns true without setting the global RUNNING_WRITER bit. This breaks the core mutual-exclusion guarantee: the caller is told it has a write lock, but other threads can still hold or acquire read locks at the same time. This vulnerability is fixed in 1.3.7.

Publish Date: 2026-06-24

URL: CVE-2026-54905

CVSS 3 Score Details (5.3)

Base Score Metrics:

  • Exploitability Metrics:
    • Attack Vector: Local
    • Attack Complexity: Low
    • Privileges Required: Low
    • User Interaction: None
    • Scope: Unchanged
  • Impact Metrics:
    • Confidentiality Impact: Low
    • 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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Dominant language
Ruby
Stars
5
Forks
21
No merged PRs in 30d

Contributor guide

Open the contributing guide

First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

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