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

Q: How do I fix CVE-2026-54904?

concurrent ruby: upgrade to 1.3.7. Exact commands for each OS are on this page.

Q: Is CVE-2026-54904 being exploited?

CVE-2026-54904 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-54904 affect?

CVE-2026-54904 affects concurrent ruby. Severity is high (CVSS 7.5). 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 AtomicRefe

Q: How urgent is CVE-2026-54904?

Priority 49/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

HIGH 7.5REMOTEUPGRADE

CVE-2026-54904 is a high-severity flaw (CVSS 7.5) affecting concurrent ruby. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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, wh

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 48%)
CISA exploited list	No
Weakness	CWE-835
Published	2026-06-24
Last modified	2026-10-25

Publisher (CNA): GitHub, Inc. · Vendor: rubyconcurrency

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-24 17:17 UTCPublished CVE record published
2026-10-25 22:10 UTCUpdated Record last modified

rubyconcurrency concurrent ruby UPGRADE

Affected: < 1.3.7

Fixed in: 1.3.7

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy concurrent-ruby || rpm -q concurrent-ruby || concurrent-ruby --version

2. UPGRADE to 1.3.7 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade concurrent-ruby

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade concurrent-ruby

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-54904?

concurrent ruby: upgrade to 1.3.7. Exact commands for each OS are on this page.

Is CVE-2026-54904 being exploited?

CVE-2026-54904 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-54904 affect?

CVE-2026-54904 affects concurrent ruby. Severity is high (CVSS 7.5). 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 AtomicRefe

How urgent is CVE-2026-54904?

Priority 49/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

Ruby vulnerabilities

Related CVEs

CVE-2026-54906 CRITICAL 9.8 UPGRADE concurrent-ruby is a modern concurrency tools for Ruby
CVE-2026-54905 MEDIUM 5.5 UPGRADE concurrent-ruby is a modern concurrency tools for Ruby

References

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