CVE-2026-18113 Concrete CMS 9.0 to 9.5.2 is vulnerable to Stored XSS in the Top Navigation Bar Block via Dropdown Child Page Names
Attackers can inject malicious scripts via page names in the Top Navigation Bar block, allowing execution in victim browsers with their privileges.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-18113?
CVE-2026-18113 is a high-severity cross-site scripting vulnerability in Concrete CMS, published on 15 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Official description
In Concrete CMS 9.0 to 9.5.2, the Top Navigation Bar block did not HTML-escape dropdown child page names before writing them into the page, so a user who could create or rename pages could store a script through a child page name and have it run in the browser of any visitor, editor, or administrator who viewed the navigation and opened the affected dropdown. In the Concrete CMS origin, the script executed with the victim's privileges and could read same-origin content or perform actions available to that user. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 7.5 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks labixiaoxin97 for reporting.
Weakness: CWE-79
Which versions are affected by CVE-2026-18113?
How do I fix CVE-2026-18113?
No fix has been published for CVE-2026-18113 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-18113 being exploited?
There is no known exploitation of CVE-2026-18113 in the wild and no public exploit code.
Sources
Also known as GHSA-fw3h-3q77-4fjj.