{"cve":"CVE-2026-81911","nvd":{"published":"2026-09-11T20:19:13.687","modified":"2026-09-18T19:00:06.357","status":"Analyzed","description":"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.","cvss_v4":{"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","score":5.8},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N","score":5.4},"cwes":["CWE-79"],"references":["https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes"],"products":["concretecms:concrete_cms"],"source":"nvd","synced_at":"2026-10-19T22:53:43.293028046+00:00"},"epss":{"cve":"CVE-2026-81911","score":0.00237,"percentile":0.14799,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}