EUVD-2026-76447
GHSA-8c9r-46mw-f22c
Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Stored XSS requires PR:H (board-editor role) and UI:R (victim views board); S:C because payload executes in arbitrary users' browsers enabling session theft.
Primary rating from Vendor (ConcreteCMS).
CVSS VectorVendor: ConcreteCMS
Lifecycle Timeline
1DescriptionCVE.org
Concrete CMS versions 9.0.0 to 9.5.2 is vulnerable to Stored XSS in Board Custom Slot dialog. The custom_slot save_template endpoint authorizes the request only against the target board instance (canEditBoardContents()) and then persists the client-supplied selectedTemplateOption[collection] verbatim, rather than rebuilding the content object collection server-side and verifying that each item belongs to the authorized board's data pool. A user with permission to edit the contents of at least one board instance can therefore store a forged summary object whose description field carries a JavaScript-bearing HTML payload. The default summary template renders the description field without output encoding, so the payload executes in the browser of any user who views the affected board slot, including anonymous front-end visitors and dashboard users who preview the resulting rule or block. This can enable session or action takeover and escalation toward an administrator. Concrete CMS versions below 9 do not include the Boards feature and are not affected. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 5.8 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:L/VA:L/SC:N/SI:N/SA:N. Thanks riodrwn for reporting.
AnalysisAI
Stored XSS in Concrete CMS 9.0.0-9.5.2 allows a user with board-editing permissions to inject arbitrary JavaScript into the description field of a summary object via the Board Custom Slot's save_template endpoint, which accepts the raw client-supplied selectedTemplateOption[collection] parameter without server-side validation or sanitization. The default summary template renders the description field without output encoding, so the stored payload fires in the browser of every subsequent visitor to the affected board slot - including unauthenticated front-end users and dashboard administrators. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The attacker must hold board-editing permission (`canEditBoardContents()`) on at least one Concrete CMS board instance - a role that typically maps to a content editor or site manager account rather than a standard subscriber (CVSS PR:H). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor-assigned CVSS 4.0 vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:L/VA:L/SC:N/SI:N/SA:N yields a score of 5.8 (Medium). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade to Concrete CMS 9.5.3 or later, which resolves the vulnerability by properly validating and rebuilding the `selectedTemplateOption[collection]` server-side and ensuring output encoding in the summary template. … Detailed patch versions, workarounds, and compensating controls in full report. |
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External POC / Exploit Code
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