CVE-2026-18119

Critical

Description

Concrete CMS below 9.5.3 did not sanitize custom style values in the Block Design dialog before writing them into page CSS via a DOM sink, permitting stored cross-site scripting. An editor-level user could execute script in an administrator's session and escalate privileges. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 7.0 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:L/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks Nguyen Manh Thuan for reporting.

SeverityCritical

CVSS9.0

Exploit probability—

Product

Concretecms Concrete Cms

PublishedSep 14, 2026

First seenSep 14, 2026

Weakness typeCWE-79Cross-site scripting (XSS)

How to fix

Update

concretecms concrete_cms9.5.3 or later

Vendor advisories

documentation.concretecms.org/developers/introduction/version-history/953-release-notes

Affected products

Product	Affected versions	Fixed in
concretecms concrete_cms	v < 9.5.3	9.5.3

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