CVE-2026-54905
This vulnerability is fixed in 1.3.7.
Does this matter?
Lower severity and a low EPSS score (0.15%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 4.0
- 2.0 LOWCVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.15% probability · 5th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-128
- Affected
- rubyconcurrency/concurrent ruby
- Source
- security-advisories@github.com
References
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.