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Concurrent RubyApplication · Rubyconcurrency

CVE-2026-54906

CRITICAL · 9.8 CVSS v3.1 Published 2026-06-24
Fix available
A fix is available. Upgrade to 1.3.7 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click 8 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The concurrent-ruby gem versions prior to 1.3.7 have two synchronization bugs in Concurrent::ReadWriteLock. First, release_write_lock lacks thread ownership verification, allowing any thread to release a write lock held by another thread, permitting a second writer into the critical section. Second, release_read_lock decrements the shared counter even when no read lock is held, corrupting state from 0 to -1 and causing Concurrent::ResourceLimitError on subsequent read acquisition attempts.

MitigationUpgrade concurrent-ruby to version 1.3.7 or later to obtain the fixed implementation that properly validates thread ownership and lock state.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Concurrent RubyApplication
Affected:< 1.3.7

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed concurrent-ruby version
    Run 'gem list concurrent-ruby' or inspect the version in your Gemfile.lock under the concurrent-ruby entry
    Affected if The version listed is below 1.3.7 (e.g., 1.3.6, 1.3.0, etc.)
  2. Search for Concurrent::ReadWriteLock usage
    Search your codebase for references to 'Concurrent::ReadWriteLock' using grep or your IDE's search (e.g., grep -r 'Concurrent::ReadWriteLock' .)
    Affected if Your code instantiates or uses Concurrent::ReadWriteLock objects
  3. Check for release_write_lock calls
    Search your codebase for method calls to 'release_write_lock' (e.g., grep -r 'release_write_lock' .)
    Affected if Your code calls release_write_lock on ReadWriteLock instances
  4. Check for release_read_lock calls
    Search your codebase for method calls to 'release_read_lock' (e.g., grep -r 'release_read_lock' .)
    Affected if Your code calls release_read_lock on ReadWriteLock instances

You are affected if you have concurrent-ruby version below 1.3.7 AND your codebase uses Concurrent::ReadWriteLock with release_write_lock or release_read_lock methods called from multiple threads.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 1.3.7 or later
Fixed in 1.3.7
Interim mitigation

Upgrade concurrent-ruby to version 1.3.7 or later to obtain the fixed implementation that properly validates thread ownership and lock state.

Recommended fix High confidence

concurrent-ruby version 1.3.7

  1. Check current version by running: gem list concurrent-ruby
  2. Update Gemfile to specify: gem 'concurrent-ruby', '~> 1.3.7'
  3. Run: bundle update concurrent-ruby
  4. Alternatively, update directly: gem install concurrent-ruby -v 1.3.7
  5. Verify the fix by running: ruby -e "require 'concurrent'; puts Concurrent::VERSION" to confirm version 1.3.7 or later is installed

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Concurrent Ruby Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing6.0 h
  • Review / QA3.0 h
14.0 hours of engineering $2,400
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-54906 in production — separate from our analysis above.

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What belongs here
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  • Version or environment caveats, and links to real fixes
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