Vulnerability in concurrent-ruby (CVE-2026-54905)
Summary
Vulnerability in concurrent-ruby (CVE-2026-54905). Confidential information can be exposed externally. Exploitable via WRITE_LOCK_HELD. Mitigation: upgrade to 1.3.7 or later.
Original description
The description as published by the source.
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.
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-54905 has been found in concurrent-ruby.
Attackers can target a specific entry point like WRITE_LOCK_HELD over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 5.5/10.
What to do: upgrade concurrent-ruby to 1.3.7 or later.
If unsure, ask your IT team or search "concurrent-ruby CVE-2026-54905" on the vendor's site.
CVE-2026-54905 (concurrent-ruby) — CWE-128 / CVSS v3 5.5
Attack vector: local / no user interaction
Attack surface: WRITE_LOCK_HELD / try_write_lock / true / RUNNING_WRITER
Patched: 1.3.7 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-128) exists in concurrent-ruby. Attackers reach the vulnerable code path via WRITE_LOCK_HELD.
Check the vendor advisory for the affected versions of concurrent-ruby. Attack surface: WRITE_LOCK_HELD / try_write_lock / true / RUNNING_WRITER.
Severity: Medium (CVSS 5.5/10). Confidential information can be exposed externally.
Update to 1.3.7.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'concurrent-ruby' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'concurrent-ruby' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
concurrent-rubyを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade concurrent-ruby to 1.3.7ステージング環境で 1.3.7 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-54905 ruby-concurrent
- Ubuntu UBUNTU-CVE-2026-54905 ruby-concurrent
References
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- web github.com
- web github.com
- web cve.org