Concurrent Ruby: ReadWriteLock allows wrong-thread write release and stray read-release counter corruption

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

2.1 · CVSS:4.0/AV:L/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-54906: 0.16% estimated exploitation activity in the next 30 days; percentile 5.25 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Concurrent::ReadWriteLock#releasewritelock 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#releasereadlock 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. It should not be framed as an authorization bypass; the lock is an in-process concurrency primitive, not an access-control boundary. Version Software: concurrent-ruby Version: 1.3.6 Commit: 7a1b78941c081106c20a9ca0144ac73a48d254ab Details releasewritelock checks only whether the global counter indicates that a writer is running. It does not track or…

Published by the source

19 Jun 2026, 20:47 UTC

Last modified by the source

19 Jun 2026, 20:47 UTC

Source last checked

26 Oct 2026, 15:52 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-6wx8-w4f5-wwcr

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# Patch Next advisory brief: CVE-2026-54906

Advisory: Concurrent Ruby: ReadWriteLock allows wrong-thread write release and stray read-release counter corruption
IDs: CVE-2026-54906, GHSA-6wx8-w4f5-wwcr
Record: https://patchnext.com/advisories/cve-2026-54906 (revision 1, source checked 26 Oct 2026, 15:52 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: concurrent-ruby 1.3.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems concurrent-ruby: affected < 1.3.7; fixed in 1.3.7

## Suggested inspection (read-only)
- RubyGems concurrent-ruby: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on concurrent-ruby.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-6wx8-w4f5-wwcr (GitHub-reviewed advisory GHSA-6wx8-w4f5-wwcr lists affected ranges: RubyGems concurrent-ruby >=0 <1.3.7)

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