CVE-2026-54905: concurrent-ruby is a modern concurrency tools for Ruby

Q: How do I fix CVE-2026-54905?

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

Q: Is CVE-2026-54905 being exploited?

CVE-2026-54905 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-2026-54905 affect?

CVE-2026-54905 affects concurrent ruby. Severity is medium (CVSS 5.5). concurrent-ruby is a modern concurrency tools for Ruby. Prior to 1.3.7, Concurrent::ReentrantReadWriteLock can incorrectly grant a write lock after one thread acquires the read lock 32,768 times. The lock stores a thread's local read and wr

Q: How urgent is CVE-2026-54905?

Priority 20/100. No elevated risk signals yet.

Routine

MEDIUM 5.5UPGRADE

CVE-2026-54905 is a medium-severity flaw (CVSS 5.5) 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::ReentrantReadWriteLock can incorrectly grant a write lock after one thread acquires the read lock 32,768 times. The lock stores a thread's local read and write hold counts in one integer. The low 15 bits are used for the read hold count, and bit 15 is used as WRITE_LOCK_HELD. After 32,768 reentrant read acquisitions, the local read count crosses into the write-loc

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	5.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 96%)
CISA exploited list	No
Weakness	CWE-128
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-2026-54905?

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

Is CVE-2026-54905 being exploited?

CVE-2026-54905 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-2026-54905 affect?

CVE-2026-54905 affects concurrent ruby. Severity is medium (CVSS 5.5). concurrent-ruby is a modern concurrency tools for Ruby. Prior to 1.3.7, Concurrent::ReentrantReadWriteLock can incorrectly grant a write lock after one thread acquires the read lock 32,768 times. The lock stores a thread's local read and wr

How urgent is CVE-2026-54905?

Priority 20/100. No elevated risk signals yet.

Software pages

Ruby vulnerabilities

Related CVEs

CVE-2026-54904 HIGH 7.5 UPGRADE concurrent-ruby is a modern concurrency tools for Ruby
CVE-2026-54906 CRITICAL 9.8 UPGRADE concurrent-ruby is a modern concurrency tools for Ruby

References

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