CVE-2026-54905: concurrent-ruby: `ReentrantReadWriteLock` read-count overflow grants a write lock without exclusivity

mediumCVSS 5.5CVE-2026-54905

CSIRTS triage

vendor: concurrent-ruby product: concurrent-rubyOther

What: A read-count overflow in `ReentrantReadWriteLock` can grant a write lock without exclusivity.
Who is affected: Users of concurrent-ruby are affected.
Urgency: Remediation is medium priority due to the moderate severity rating.
Action: Update to the latest version of concurrent-ruby.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 5.5
Published: 2026-06-09
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-54905

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-549050.11% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 1% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-54905	coverage & exploitation status	NVD · CVE.org

Recent advisories for concurrent-ruby

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

criticalCVE-2026-54906: concurrent-ruby: ReadWriteLock allows wrong-thread write release and stray read-release counte…msrc · 2026-06-09