Vulnerability · Published Jun 24, 2026 · Assigned by GitHub_M
CVE-2026-54905concurrent-ruby: `ReentrantReadWriteLock` read-count overflow grants a write lock without exclusivity
Low 2.0
In plain English
A low-severity security flaw in concurrent-ruby from ruby-concurrency. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 4% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | ruby-concurrent | no fix listed | DEBIAN-CVE-2026-54905 |
| Debian:13 | ruby-concurrent | no fix listed | DEBIAN-CVE-2026-54905 |
| Debian:14 | ruby-concurrent | 1.3.7-1 | DEBIAN-CVE-2026-54905 |
| RubyGems | concurrent-ruby | 1.3.7 | GHSA-wv3x-4vxv-whpp |
| Ubuntu:22.04:LTS | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54905 |
| Ubuntu:24.04:LTS | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54905 |
| Ubuntu:25.10 | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54905 |
| Ubuntu:26.04:LTS | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54905 |
| Ubuntu:26.10 | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54905 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| ruby-concurrency | concurrent-ruby | < 1.3.7 |
Weakness: CWE-128 · Vector: 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