GHSA-x76w-8c62-48mg CVE-2026-56384
Craft CMS: Authenticated "assets/preview-thumb" discloses signed fallback transform preview link to CP users without asset-view permission
Medium
Packagist
- Severity
- 0.0 / 10
- Medium · CVSS 4.0
- Exploit chance (EPSS)
- 0.33%
- Chance of exploitation in the next 30 days. Higher than 26.30% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-200 Exposure of Sensitive Information to an Unauthorized Actor
- CWE-862 Missing Authorization
- Fix
4.17.8- Upgrade craftcms/cms to this version or later
Description
Summary
A user with Control Panel access but without permission to view a target private asset can call assets/preview-thumb and receive preview HTML that contains a signed fallback transform link for that private asset.
Details
Root-cause analysis:
- The endpoint accepts an attacker-controlled
assetId. - Asset is resolved, and thumbnail HTML is returned.
- No explicit asset-view permission check is performed before preview generation.
Impact
Type:
- Missing authorization
- Unauthorized preview-link disclosure
Affected deployments:
- Craft sites with control panel users who have partial permissions and private assets.
Security consequence:
- A control panel user without asset-view permission can still obtain signed preview transform link data for private assets.
- This may increase private asset exposure risk depending on deployment and endpoint chaining.
Resources
https://github.com/craftcms/cms/commit/d30df3112220db1ffd6726a3ed11857014c7fb27
Affected versions
Packagist
| Package | Vulnerable | Fixed in |
|---|---|---|
| craftcms/cms | >= 4.0.0-RC1, < 4.17.8 |
4.17.8 |
| craftcms/cms | >= 5.0.0-RC1, < 5.9.14 |
5.9.14 |
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.
craftcms/cms Packagist → 4.17.8
- composer
composer require craftcms/cms:^4.17.8
Severity breakdown
CVSS 4.0 0.0
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- None
- Privileges required
- Low
- User interaction
- None
- Confidentiality (vulnerable system)
- Low
- Integrity (vulnerable system)
- None
- Availability (vulnerable system)
- None
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
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-200: Exposure of Sensitive Information to an Unauthorized Actor
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
How to prevent it
- Architecture and Design: Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
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
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-7vrx-9684-xrf2 Craft CMS stores arbitrary content provided by unauthenticated users in session files | Medium Known exploited | Also affects craftcms/cms |
| GHSA-f3gw-9ww9-jmc3 Craft CMS Allows Remote Code Execution | Critical Known exploited | Also affects craftcms/cms |
| GHSA-x684-96hh-833x Craft CMS has a potential RCE with a compromised security key | High Known exploited | Also affects craftcms/cms |
| GHSA-2p6p-9rc9-62j9 Craft CMS has potential RCE when PHP `register_argc_argv` config setting is enabled | Critical Known exploited | Also affects craftcms/cms |
| GHSA-wg23-69c2-gjc8 Craft CMS: Passkey login accepts replayed WebAuthn assertions | Medium | Also affects craftcms/cms |
| GHSA-957r-qf9p-67xw Craft CMS: Arbitrary file read via SplFileObject in non-sandboxed template contexts | Medium | Also affects craftcms/cms |
| GHSA-596p-6jv8-775v Craft CMS: Authenticated leak of secret environment variables | Medium | Also affects craftcms/cms |
| GHSA-xxpx-f366-4xpq Craft CMS: Authorization bypass: view-only Categories user can modify category structure via structures/move-element | Medium | Also affects craftcms/cms |
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