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

Description

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.

Scores

EPSS (exploitation in 30 days)

0.26% · top 83% of all CVEs (6 Nov 2026)

CISA SSVC

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

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.3.

Weakness

• CWE-79 Improper Neutralization of Input During Web Page Generation (opens in a new tab)All about CWE-79 and its CVEs

Affected products

• Concrete CMS · Concrete CMS

  • affected 8.3.0 – ≤ 9.5.2

References (1)

• https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes (opens in a new tab)release-notes

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-18116](https://trackcve.app/badge/CVE-2026-18116.svg)](https://trackcve.app/cve/CVE-2026-18116)

Record last updated 15 Sept 2026, 13:39 UTC.