Vulnerability in concrete5/concrete5 (CVE-2026-8204)
Summary
Vulnerability in concrete5/concrete5 (CVE-2026-8204). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 9.5.1 or later.
Original description
The description as published by the source.
Concrete CMS 9.5.0 and below is vulnerable to authorization Bypass in the Calendar Event Frontend Dialog which can allow cross-calendar data disclosure. A public calendar block can be used as a pivot point to access private calendar data.
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-2026-8204 has been found in concrete5/concrete5.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade concrete5/concrete5 to 9.5.1 or later.
If unsure, ask your IT team or search "concrete5/concrete5 CVE-2026-8204" on the vendor's site.
CVE-2026-8204 (concrete5/concrete5) — CWE-639 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 9.5.1 — 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-639) exists in concrete5/concrete5.
Check the vendor advisory for the affected versions of concrete5/concrete5.
Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.
Update to 9.5.1.
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 'concrete5/concrete5' . 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 'concrete5/concrete5' . | 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
concrete5/concrete5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 concrete5/concrete5 to 9.5.1ステージング環境で 9.5.1 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
References
- advisory nvd.nist.gov
- package github.com
- web documentation.concretecms.org
- web github.com