Concurrent Ruby : AtomicReference#update livelocks when the stored value is Float::NAN

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-54904: 0.67% estimated exploitation activity in the next 30 days; percentile 52.15 (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::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 compareandset(oldvalue, newvalue) succeeds. - Numeric compareandset, which checks old == oldvalue before attempting the underlying atomic swap. - 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. Version Software: concurrent-ruby Version: 1.3.6 Commit: 7a1b78941c081106c20a9ca0144ac73a48d254ab Details AtomicReference#update retries until compareandset returns true: For numeric expected values, compareandset uses numeric equality before attempting the underlying atomic compare-and-set:…

Published by the source

19 Jun 2026, 20:47 UTC

Last modified by the source

5 Aug 2026, 17:36 UTC

Source last checked

26 Oct 2026, 15:52 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-h8w8-99g7-qmvj

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-54904

Advisory: Concurrent Ruby : `AtomicReference#update` livelocks when the stored value is `Float::NAN`
IDs: CVE-2026-54904, GHSA-h8w8-99g7-qmvj
Record: https://patchnext.com/advisories/cve-2026-54904 (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: High (CVSS 8.2)
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-h8w8-99g7-qmvj (GitHub-reviewed advisory GHSA-h8w8-99g7-qmvj lists affected ranges: RubyGems concurrent-ruby >=0 <1.3.7)

Commands are suggestions: review each one before running it.