GHSA-q6wp-fr43-gm9v CVE-2026-107850
Contao: Improper access control in the preview links module
- Severity
- 4.3 / 10
- Medium · CVSS 3.1
- Exploit chance (EPSS)
- 0.19%
- Chance of exploitation in the next 30 days. Higher than 9.03% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Fix
5.7.12- Upgrade contao/core-bundle to this version or later
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one grants front end preview of the target page with showUnpublished and with no page permission check at all, so unpublished or embargoed content becomes readable by a user who has no rights on those pages, and by anyone that user forwards the URL to.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 versions
Packagist
| Package | Vulnerable | Fixed in |
|---|---|---|
| contao/core-bundle | >= 5.7.1, < 5.7.12 |
5.7.12 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
contao/core-bundle Packagist → 5.7.12
- composer
composer require contao/core-bundle:^5.7.12
Severity breakdown
CVSS 3.1 4.3
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- None
- Availability
- None
Weakness
CWE-639: Authorization Bypass Through User-Controlled Key
The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.
How to prevent it
- Architecture and Design: For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.
- Architecture and Design, Implementation: Make sure that the key that is used in the lookup of a specific user's record is not controllable externally by the user or that any tampering can be detected.
- Architecture and Design: Use encryption in order to make it more difficult to guess other legitimate values of the key or associate a digital signature with the key so that the server can verify that there has been no tampering.
CWE-862: Missing Authorization
The product does not perform an authorization check when an actor attempts to access a resource or perform an action.
How to prevent it
- Architecture and Design: Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
- Architecture and Design: Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor [REF-7].
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
- Architecture and Design: For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page. One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
- System Configuration, Installation: Use the access control capabilities of your operating system and server environment and define your access control lists accordingly. Use a "default deny" policy when defining these ACLs.
References
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-9ff2-p842-45wq Contao: Cross-site request forgery in custom backend actions | Low | Also affects contao/core-bundle |
| GHSA-5974-gfqc-wrcm Contao: Improper access control in the table access voter | Medium | Also affects contao/core-bundle |
| GHSA-mrvp-7wmx-5m4h Contao: Path traversal in the images controller | Medium | Also affects contao/core-bundle |
| GHSA-mfxh-vp55-7gc6 Contao: The registration module re-sends activation mails | Medium | Also affects contao/core-bundle |
| GHSA-x2rp-9qf7-2fmq Contao: Protected page content is disclosed to anonymous visitors after contao.search.index_protected is disabled | Medium | Also affects contao/core-bundle |
| GHSA-grm4-wm43-9jh5 Contao: Possible path traversal in job download URIs | Low | Also affects contao/core-bundle |
| GHSA-87mg-5grr-rhwh Contao: Server-Side Request Forgery (SSRF) via Unvalidated RSS Feed URL in Feed Reader Module | Low | Also affects contao/core-bundle |
| GHSA-3mr9-p497-58f6 Contao crawler leaks auth credentials to external hosts | Low | Also affects contao/core-bundle |
MergeHarbor checks every repository's dependencies against this database, ranks what matters by exploitability and reachability, routes it to the owning team and opens the fix pull request.
Check your repos with MergeHarbor