# CVE-2026-18110: Missing authorization in Concrete CMS

> Unauthenticated attackers can enumerate all backend user accounts, including super-admins, via an unprotected autocomplete endpoint in Concrete CMS.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Sep 2026
- **Updated:** 22 Sep 2026
- **Also known as:** GHSA-7hmf-f7jv-m4xw

## What is CVE-2026-18110?

CVE-2026-18110 is a high-severity missing authorization vulnerability in Concretecms Concrete Cms, published on 15 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Concrete CMS 9 (9.0.0 through 9.5.2) does not perform an authorization check on the user selector autocomplete endpoint (/ccm/system/user/autocomplete), which backs the "Preview as User" panel and other user-selector components. The endpoint validates only a CSRF-style access token that is bound to the selector's display options rather than to the caller's identity or permissions, and that token is issued to anonymous visitors because the selector renders without an authorization check. Because an empty query resolves to a match-all filter, an unauthenticated attacker can submit an empty search and paginate the results to enumerate every backend account, disclosing the internal user ID, username, and email address of all administrative users, including the super-administrator (user ID 1). No password hashes or session material are disclosed The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 8.7 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks thirtythree and YesWeHack for reporting.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2026-18110?

It affects 1 product.


Products: Concretecms Concrete Cms.

## How do I fix CVE-2026-18110?

No fix has been published for CVE-2026-18110 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-18110 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-18110 exists.

Public exploit code:

- Proof-of-Concept for CVE-2026-18110 (github_poc): https://github.com/flenz00/CVE-2026-18110-PoC
- Concrete CMS - User Enumeration (nuclei): http/cves/2026/CVE-2026-18110.yaml

## Other vulnerabilities in Concretecms Concrete Cms

- [CVE-2023-48648](https://insights.sbomify.com/CVE-2023-48648/): Concrete CMS allows unauthorized access because directories can be created with insecure permissions (critical 9.8)
- [CVE-2022-21829](https://insights.sbomify.com/CVE-2022-21829/): Code injection in concrete CMS (critical 9.8)
- [CVE-2021-22958](https://insights.sbomify.com/CVE-2021-22958/): Server-Side Request Forgery vulnerability in concrete5 (critical 9.8)
- [CVE-2021-40098](https://insights.sbomify.com/CVE-2021-40098/): Path traversal in n/a (critical 9.8)
- [CVE-2026-8134](https://insights.sbomify.com/CVE-2026-8134/): Concrete CMS Vulnerable to Relative Path Traversal (critical 9.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18110 and fix it if it is affected.

What it is: CVE-2026-18110 is a high-severity missing authorization vulnerability in Concretecms Concrete Cms, published on 15 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-18110 exists.

Affected product: Concretecms 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-2026-18110/ (Markdown: https://insights.sbomify.com/CVE-2026-18110/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18110
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18110
- OSV: https://osv.dev/vulnerability/CVE-2026-18110

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18110/
Summaries are generated and may contain mistakes; the official description above is the record.