# 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.

- **Severity:** High 7.5 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Sep 2026
- **Updated:** 20 Sep 2026
- **Also known as:** GHSA-fw3h-3q77-4fjj

## 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 (Improper Neutralization of Input During Web Page Generation)

## 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.

## Is CVE-2026-18113 being exploited?

There is no known exploitation of CVE-2026-18113 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18113 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-18113 in the wild and no public exploit code.

Affected product: Concrete CMS. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-18113/ (Markdown: https://insights.sbomify.com/CVE-2026-18113/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18113
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18113
- OSV: https://osv.dev/vulnerability/CVE-2026-18113

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18113/
Summaries are generated and may contain mistakes; the official description above is the record.