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

Quick assessment

Affected
ruby-concurrency concurrent-ruby
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

ruby-concurrency Concurrent Ruby是ruby-concurrency组织开源的一款并发编程工具库。 ruby-concurrency concurrent-ruby 1.3.7之前版本存在数字错误漏洞，该漏洞源于Concurrent::ReentrantReadWriteLock锁在读计数器达到32768次后可能错误授权写锁，导致破坏核心互斥保证。

AI Predicted 7.5 Difficulty: Moderate EPSS 0.15% · P4

Possible ATT&CK Techniques 1 AI

T1003 · OS Credential Dumping

Affected Version Matrix 1

VendorProduct Version RangeStatus
ruby-concurrency concurrent-ruby < 1.3.7 affected
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I. Basic Information for CVE-2026-54905

Vulnerability Information
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Vulnerability Title
concurrent-ruby: `ReentrantReadWriteLock` read-count overflow grants a write lock without exclusivity
Source: CVE Program / CVE List V5
Vulnerability Description
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-lock bit. try_write_lock then treats the thread as already holding a write lock and returns true without setting the global RUNNING_WRITER bit. This breaks the core mutual-exclusion guarantee: the caller is told it has a write lock, but other threads can still hold or acquire read locks at the same time. This vulnerability is fixed in 1.3.7.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
超界折返处理错误
Source: CVE Program / CVE List V5
Vulnerability Title
ruby-concurrency Concurrent Ruby 数字错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
ruby-concurrency Concurrent Ruby是ruby-concurrency组织开源的一款并发编程工具库。 ruby-concurrency concurrent-ruby 1.3.7之前版本存在数字错误漏洞，该漏洞源于Concurrent::ReentrantReadWriteLock锁在读计数器达到32768次后可能错误授权写锁，导致破坏核心互斥保证。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
ruby-concurrency concurrent-ruby < 1.3.7 -

II. Public POCs for CVE-2026-54905

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III. Intelligence Information for CVE-2026-54905

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Vendor Advisories for CVE-2026-54905 (1)

Same Patch Batch · ruby-concurrency · 2026-06-24 · 3 CVEs total

CVE-2026-54904 8.2 HIGH concurrent-ruby: `AtomicReference#update` livelocks when the stored value is `Float::NAN`
CVE-2026-54906 concurrent-ruby: ReadWriteLock allows wrong-thread write release and stray read-release co

IV. Related Vulnerabilities

Same product: concurrent-ruby
Same vendor: ruby-concurrency
Same weakness: CWE-128

V. Comments for CVE-2026-54905

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