# CVE-2026-54904: ruby-concurrent: concurrent-ruby is a modern concurrency tools for Ruby

CVE-2026-54904 is fixed in ruby-concurrent on 1 platform by DEBIAN-CVE-2026-54904 (version 1.3.7-1), released July 3, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-54904
- Priority: High
- CVSS: 7.5 (high)
- EPSS: 0.0067
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 24, 2026

## Description

concurrent-ruby is a modern concurrency tools for Ruby. Prior to 1.3.7, 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 compare_and_set(old_value, new_value) succeeds; Numeric compare_and_set, which checks old == old_value before attempting the underlying atomic swap.; and 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. This vulnerability is fixed in 1.3.7.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | ruby-concurrent Debian 14 | 1.3.7-1 | [DEBIAN-CVE-2026-54904](https://patchblox.com/security/data/fix/linux/debian-cve-2026-54904.md) | Jul 3, 2026 |

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