Vulnerability · Published Sep 14, 2026 · Assigned by ConcreteCMS

CVE-2026-18119Concrete CMS below 9.5.3 is vulnerable to Stored XSS via unsanitized inline block custom style values

High 7.0

In plain English

A high-severity cross-site scripting in Concrete CMS from Concrete CMS. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 40% of all known vulnerabilities).

Severity (CVSS 4.0)7.0High

Exploit odds (30 days)0.5%top 59.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected products (as reported)

Vendor	Product	Versions
Concrete CMS	Concrete CMS	5.0.0 – through 9.5.2

Weakness: CWE-79 · 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

References

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