CVE-2026-18426

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.

CVSS v3 6.5 MEDIUM

6.5^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required LOW

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes	Broken Link

Configurations

Configuration 1 (hide)

cpe:2.3:a:concretecms:concrete_cms:*:*:*:*:*:*:*:*

History

21 Sep 2026, 17:53

Type	Values Removed	Values Added
CPE		cpe:2.3:a:concretecms:concrete_cms::::::::
References	~~() https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes -~~	() https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes - Broken Link
CVSS	v2 : ~~unknown~~ v3 : ~~unknown~~	v2 : unknown v3 : 6.5
First Time		Concretecms Concretecms concrete Cms

Information

Published : 2026-09-15 21:16

Updated : 2026-09-21 17:53

NVD link : CVE-2026-18426

Mitre link : CVE-2026-18426

CVE.ORG link : CVE-2026-18426

JSON object : View

Products Affected

concretecms

concrete_cms

CWE

CWE-862

Missing Authorization

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