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High severity7.5NVD Advisory· Published Jun 24, 2026· Updated Aug 5, 2026

CVE-2026-54904

CVE-2026-54904

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.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
concurrent-rubyRubyGems
< 1.3.71.3.7

Affected products

57

Patches

Vulnerability mechanics

References

7

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