# CVE-2026-18426

## Summary

- **CVE ID:** CVE-2026-18426
- **Severity:** LOW
- **CVSS Score:** 2 (CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-862
- **Published:** Sep 15, 2026
- **Last Modified:** Sep 16, 2026

## Description

Concrete CMS 9.0.0 through 9.5.2 did not enforce a block-level edit-permission check on the Express Form block's control-management actions, which relied solely on CSRF token validation. Because the token is bound to the user and action rather than to a specific block, page, or form, an authenticated user with edit access to one Express Form could reuse a validly obtained token to add, modify, or delete controls on Express Forms they were not authorized to edit, including injecting a control whose value is later rendered as HTML to achieve stored XSS. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 2.0 with vector CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks Yat Wu for reporting.

## Affected Products

- Concrete CMS — Concrete CMS (9.0.0)

## References

- [CNA](https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.23%
- **EPSS Percentile:** 13.7

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._