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CVE-2026-18116

Concrete CMS 8.3.0 to 9.5.2 is vulnerable to Stored XSS in Calendar Event Name via Workflow Approval Notifications

Published
Last modified
published
Not listed in CISA KEV
1 proof of concept on GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: total

Summary

Concrete CMS 8.3.0 to 9.5.2 stored calendar event names without sanitization and rendered them without HTML escaping in the workflow approval and deletion notifications shown in the dashboard "Waiting For Me" block. A registered user permitted to add events to a calendar governed by an approval workflow could submit an event whose name contained a script payload, which then executed in an administrator's browser when the pending request was displayed and could be used to create a new administrator account. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 7.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks v01demort for reporting.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: total

  3. Record last updated

Affected versions

  • Concrete CMS Concrete CMS

    From 8.3.0 · through 9.5.2

References 2

documentation.concretecms.org

GitHub · EndlssNightmare/CVE-2026-18116