CVE-2026-54905
Concurrent Ruby: `ReentrantReadWriteLock` read-count overflow grants a write lock without exclusivity
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| rubygems | concurrent-ruby | < 1.3.7 | 1.3.7 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Rubyconcurrency | Concurrent Ruby | before 1.3.7 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-wv3x-4vxv-whpp
- https://github.com/ruby-concurrency/concurrent-ruby/security/advisories/GHSA-wv3x-4vxv-whpp
- https://nvd.nist.gov/vuln/detail/CVE-2026-54905
- https://github.com/rubysec/ruby-advisory-db/blob/master/gems/concurrent-ruby/CVE-2026-54905.yml
- https://www.cve.org/CVERecord/SearchResults?query=CVE-2026-54905