Contao: Improper access control in the preview links moduleGHSA-q6wp-fr43-gm9v
MEDIUMFix: contao/contao@6b483d3GHSA-q6wp-fr43-gm9v is a medium-severity (CVSS 4.3) CWE-639 vulnerability in contao/core-bundle. A fix is available for contao/core-bundle — see the affected versions and patch details below.
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-q6wp-fr43-gm9v.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-q6wp-fr43-gm9v by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
contao/core-bundleReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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one grants front end preview of the target page with showUnpublished and with no page permission check at all, so unpublished or embargoed content becomes readable by a user who has no rights on those pages, and by anyone that user forwards the URL to.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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | contao/core-bundle | ≥ 5.7.1&&< 5.7.12 | 5.7.12composer require contao/core-bundle:^5.7.12 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for contao/core-bundle, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update contao/core-bundle to 5.7.12 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-q6wp-fr43-gm9v is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.
Frequently Asked Questions
Is GHSA-q6wp-fr43-gm9v in your dependencies?
Find it across Packagist, including transitive dependencies.