concurrent-ruby: `ReentrantReadWriteLock` read-count overflow grants a write lock without exclusivity
Key facts
- Attack vector
- Local
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- Present
- Impact type
- —
- Confidentiality · integrity · availability
- Low · Low · Low
- Fix status
- Partial Red Hat: 3 without a fix
Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| ruby-concurrency | concurrent-ruby | before 1.3.7 | 1.3.7 | Patch available | CNA |
| — | concurrent-ruby (RubyGems) | before 1.3.7 | 1.3.7 | Patch available | GHSA-wv3x-4vxv-whpp |
- concurrent-ruby Vendorruby-concurrency Affected before 1.3.7 Fixed in 1.3.7 Patch available CNA
- concurrent-ruby (RubyGems) Vendor— Affected before 1.3.7 Fixed in 1.3.7 Patch available GHSA-wv3x-4vxv-whpp
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:rubyconcurrency:concurrent_ruby:*:*:*:*:*:ruby:*:* | before 1.3.7 | Vulnerable | ruby-concurrency |
- cpe:2.3:a:rubyconcurrency:concurrent_ruby:*:*:*:*:*:ruby:*:* Versions before 1.3.7 Vulnerable ·ruby-concurrency
Remediation
- Fix · CNA concurrent-ruby (ruby-concurrency) Fixed in 1.3.7
- Fix · GHSA-wv3x-4vxv-whpp concurrent-ruby (RubyGems) Fixed in 1.3.7 Advisory →
Vendor assessments
Red Hat
Red Hat rating: Low. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat 3scale API Management Platform 2 | Affected | No fix yet: Fix deferred |
| Red Hat OpenStack Platform 17.1 | Affected | No fix yet: Fix deferred |
| Red Hat Satellite 6 | Affected | No fix yet: Fix deferred |
Timeline
- 2026-10-02 Threatist record created from CVE-2026-54905
- 2026-10-03 Alias added: GHSA-wv3x-4vxv-whpp
References
Advisory 2
More ruby-concurrency Concurrent Ruby vulnerabilities
- TI-2026-39676 concurrent-ruby: `AtomicReference#update` livelocks when the stored value is `Float::NAN` CVSS 4.0HIGH 8.2
- TI-2026-39678 concurrent-ruby: ReadWriteLock allows wrong-thread write release and stray read-release counter corruption CVSS 4.0LOW 2.1
Sources
- CVE-2026-54905 · CVE Program
- CVE-2026-54905 · NVD
- FIRST EPSS
- GHSA-wv3x-4vxv-whpp · GitHub Advisory Database · CC BY 4.0
- CVE-2026-54905 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences