Vulnerability · Published Jun 24, 2026 · Assigned by GitHub_M
CVE-2026-54904concurrent-ruby: `AtomicReference#update` livelocks when the stored value is `Float::NAN`
High 8.2
In plain English
A high-severity infinite loop 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 0.7% (higher than 52% 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::AtomicReference#update can enter a permanent busy retry loop when the current value is Float::NAN. The issue is caused by the interaction between AtomicReference#update, which retries until compare_and_set(old_value, new_value) succeeds; Numeric compare_and_set, which checks old == old_value before attempting the underlying atomic swap.; and Ruby NaN semantics, where Float::NAN == Float::NAN is always false. As a result, once an AtomicReference contains Float::NAN, calling #update repeatedly evaluates the caller's block and never returns. In services that store externally derived numeric values in an AtomicReference, this can cause CPU exhaustion or permanent request/job hangs. 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-2026-54904 |
| Debian:13 | ruby-concurrent | no fix listed | DEBIAN-CVE-2026-54904 |
| Debian:14 | ruby-concurrent | 1.3.7-1 | DEBIAN-CVE-2026-54904 |
| RubyGems | concurrent-ruby | 1.3.7 | GHSA-h8w8-99g7-qmvj |
| Ubuntu:22.04:LTS | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54904 |
| Ubuntu:24.04:LTS | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54904 |
| Ubuntu:25.10 | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54904 |
| Ubuntu:26.04:LTS | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54904 |
| Ubuntu:26.10 | ruby-concurrent | no fix listed | UBUNTU-CVE-2026-54904 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| ruby-concurrency | concurrent-ruby | < 1.3.7 |
Weakness: CWE-835 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
References
- https://github.com/ruby-concurrency/concurrent-ruby/security/advisories/GHSA-h8w8-99g7-qmvj x_refsource_CONFIRM
- https://github.com/ruby-concurrency/concurrent-ruby/commit/6e37e0644b83b182971dc540d2e4bee38df61386 x_refsource_MISC
- https://github.com/ruby-concurrency/concurrent-ruby/releases/tag/v1.3.7 x_refsource_MISC
- https://github.com/rubysec/ruby-advisory-db/blob/master/gems/concurrent-ruby/CVE-2026-54904.yml x_refsource_MISC