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CVE-2026-18116

6.1 · MEDIUM

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 "Wait…

Published Sep 14, 2026concretecmsCWE-79EPSS 0.26%

Overview

CVE-2026-18116 is a medium-severity vulnerability affecting concretecms concrete_cms. It was published on September 14, 2026 and has a CVSS 3.1 base score of 6.1 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 6.1, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories and patches from concretecms. Update concrete_cms to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected products

VendorProductVersionsStatus
concretecmsconcrete_cms>= 8.3.0, < 9.5.3Affected

References

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

How CyberStrike helps

Frequently asked questions

What is CVE-2026-18116?

CVE-2026-18116 is a medium-severity vulnerability affecting concretecms concrete_cms. It was published on September 14, 2026 and has a CVSS 3.1 base score of 6.1 (MEDIUM).

How severe is CVE-2026-18116?

This vulnerability has a CVSS 3.1 base score of 6.1, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-18116?

Check the references section for vendor advisories and patches from concretecms. Update concrete_cms to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-18116?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-18116 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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