# Contao: Improper access control in the preview links module

Advisory record · `GHSA-q6wp-fr43-gm9v`

- **Identifiers:** `GHSA-q6wp-fr43-gm9v` · `CVE-2026-107850` · `PKSA-7n2q-445d-xssj`
- **State:** Confirmed
- **Severity:** CVSS 4.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-639](https://cwe.mitre.org/data/definitions/639.html) · [CWE-862](https://cwe.mitre.org/data/definitions/862.html)
- **Tags:** [Broken access control](https://agentprime.io/advisories/tag/access-control.md)
- **Published:** 9 Oct 2026
- **Updated:** 9 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 9 Oct 2026, 20:53 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `contao/core-bundle` (Packagist): affected `>=5.7.1, <5.7.12`; fixed in `5.7.12`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Contao's contao/core-bundle versions 5.7.1 up to but not including 5.7.12 have a broken preview access voter registration: the service class name in services.yaml does not match the class on disk, so the ownership check is never run. A logged-in back end user whose group has the preview link module can list every preview link on the installation, including links created by others, and follow them to view unpublished pages without page permission checks. Upgrade to contao/core-bundle 5.7.12, which is the listed fixed version.

Written 31 Oct 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 4.3 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0019, the 9th percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 25 Aug 2026, 06:40 UTC: [Confirmed by Packagist](https://contao.org/en/security-advisories/improper-access-control-in-the-preview-links-module)
- 31 Oct 2026, 13:54 UTC: First seen by agentprime
- 31 Oct 2026, 13:54 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-q6wp-fr43-gm9v)

## Sources

- [GitHub Advisory Database: GHSA-q6wp-fr43-gm9v](https://github.com/advisories/GHSA-q6wp-fr43-gm9v)
- [OSV: GHSA-q6wp-fr43-gm9v](https://osv.dev/vulnerability/GHSA-q6wp-fr43-gm9v)
- <https://github.com/contao/contao/security/advisories/GHSA-q6wp-fr43-gm9v>
- <https://github.com/contao/contao/commit/6b483d380a4b2dc61432c4c697e411508f93bf91>
- <https://github.com/contao/contao>
- <https://github.com/contao/contao/releases/tag/5.7.12>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-q6wp-fr43-gm9v>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

---

The web page: <https://agentprime.io/advisories/GHSA-q6wp-fr43-gm9v/>. Everything for agents: <https://agentprime.io/llms.txt>.