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Medium

Contao: Improper access control in the preview links module

  • Disclosed: 09.10.2026
  • Updated: 11.10.2026 10:32

core-bundle/config/services.yaml registers the preview access voter with the class Contao\CoreBundle\Security\Voter\DataContainer\PreviewAccessVoter, but the class shipped on disk is named PreviewVoter. Symfony resolves the class with getReflectionClass($class, false), gets null, silently skips the interface-based autoconfiguration that would have tagged it as a voter, and the now untagged private service is removed when the container is compiled. The application boots without a warning, and the ownership rule in PreviewVoter::hasAccess() is never executed. tl_preview_link has no compensating SQL filter on createdBy, so any non-administrator back end user whose group holds the preview_link module reads every preview link on the installation and lifts the already signed share URLs straight out of the list. Following one grants front end preview of the target page, with showUnpublished and with no page permission check, to anyone at all.

Impact

A non-administrator back end user reads every preview link on the installation, including links created by administrators, and lifts the already signed share URLs out of the list. Following one grants front end preview of the target page with showUnpublished and with no page permission check at all, so unpublished or embargoed content becomes readable by a user who has no rights on those pages, and by anyone that user forwards the URL to.

Honesty caveat, stated because it bounds the severity. UpdateAction on a record owned by someone else was denied in our lab by DcaPermissionVoter, so we do not claim that a foreign preview link can be edited or deleted.

What to do

Update contao/core-bundle to version 5.7.12 or newer.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Composer package contao/core-bundle >= 5.7.1, < 5.7.12 5.7.12

References

CVSS score 4.3/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Weakness (CWE)
CWE-639, CWE-862
Platform
Composer
Package
contao/core-bundle
Disclosed
09.10.2026
Updated
11.10.2026 10:32

Sources and licenses · Edited or translated by DockRay; source rights and applicable licenses are retained.

OSV / GitHub Advisory Database - GHSA-q6wp-fr43-gm9v - CC BY 4.0

Vulnerability history: contao/core-bundle

All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (40) in the archive
Total entries
40
First → latest
12.2019 10.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • Critical 4
  • High 7
  • Medium 23
  • Low 6

Disclosures per year

Severity:
  1. Contao: Improper access control in the preview links module this entry
    Medium · 4.3 CVE-2026-107850 >= 5.7.1, < 5.7.12 5.7.12
  2. Contao affected by remote command execution through file upload
    High · 8.3 CVE-2024-45398 >= 4.0.0, < 4.13.49, >= 5.0.0, < 5.3.15, >= 5.4.0, < 5.4.3 4.13.49, 5.3.15, 5.4.3
  3. Contao: Possible cookie sharing with external domains while checking protected pages for broken links
    High · 8.3 CVE-2024-28235 >= 4.9.0, < 4.13.40, >= 5.0.0-RC1, < 5.3.4 4.13.40, 5.3.4
  4. Contao SQL injection in the file manager
    Critical · 9.8 CVE-2019-11512 >= 4.1.0, < 4.4.39, >= 4.5.0, < 4.7.5 4.4.39, 4.7.5
  5. Contao SQL injection in the backend and listing module
    Critical · 9.8 CVE-2017-16558 >= 4.0.0, < 4.4.8, >= 3.0.0, <= 3.5.30 4.4.8
  6. Cross site scripting via canonical tag in Contao
    High · 7.2 CVE-2022-24899 >= 4.13.0, < 4.13.3 4.13.3
  7. Contao CSRF Token Bypass
    High · 8.8 CVE-2019-10642 >= 4.7.0, < 4.7.3 4.7.3
  8. Contao Does Not Invalidate Existing Sessions When Password Changes
    Critical · 9.8 CVE-2019-10641 >= 4.0.0, < 4.4.37, >= 4.5.0, < 4.7.3 4.4.37, 4.7.3
  9. Contao Core directory traversal vulnerability
    High · 8.8 CVE-2017-10993 >= 4.0.0, < 4.4.1 4.4.1
  10. Contao Does Not Expire Tokens Correctly
    Critical · 9.8 CVE-2019-10643 >= 4.7.0, < 4.7.3 4.7.3
  11. Privilege escalation via form generator
    High · 8.0 CVE-2021-37627 >= 4.0.0, < 4.4.56, >= 4.5.0, < 4.9.18, >= 4.10.0, < 4.11.7 4.4.56, 4.9.18, 4.11.7
  12. Unrestricted file uploads in Contao
    High · 8.8 CVE-2019-19745 >= 4.0.0, < 4.4.46, >= 4.5.0, < 4.8.6 4.4.46, 4.8.6

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