Vulnerability · Published Jun 24, 2026 · Assigned by GitHub_M
CVE-2026-54906concurrent-ruby: ReadWriteLock allows wrong-thread write release and stray read-release counter corruption
Low 2.1
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 5% 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::ReadWriteLock#release_write_lock does not verify that the calling thread acquired the write lock. Any thread with access to the lock object can release an active write lock held by another thread. A second writer can then enter its critical section while the first writer is still running. Concurrent::ReadWriteLock#release_read_lock also decrements the shared counter even when no read lock is held. Calling it on a fresh lock changes the counter from 0 to -1, after which normal read acquisition raises Concurrent::ResourceLimitError. This is a synchronization correctness issue in the public Concurrent::ReadWriteLock API. 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-2026-54906 |
| Debian:13 | ruby-concurrent | no fix listed | DEBIAN-CVE-2026-54906 |
| Debian:14 | ruby-concurrent | 1.3.7-1 | DEBIAN-CVE-2026-54906 |
| RubyGems | concurrent-ruby | 1.3.7 | GHSA-6wx8-w4f5-wwcr |
| Ubuntu:22.04:LTS | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54906 |
| Ubuntu:24.04:LTS | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54906 |
| Ubuntu:25.10 | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54906 |
| Ubuntu:26.04:LTS | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54906 |
| Ubuntu:26.10 | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54906 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| ruby-concurrency | concurrent-ruby | < 1.3.7 |
Weakness: CWE-414, CWE-667 · Vector: CVSS:4.0/AV:L/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N