Craft CMS has IDOR via GraphQL @parseRefs

The GraphQL directive @parseRefs, intended to parse internal reference tags (e.g., {user:1:email}), can be abused by both authenticated users and unauthenticated guests (if a Public Schema is enabled) to access sensitive attributes of any element in the CMS. The implementation in Elements::parseRefs fails to perform authorization checks, allowing attackers to read data they are not authorized to view.

Vulnerability Details

craft\services\Elements::parseRefs identifies reference tags and resolves them using _getRefTokenReplacement. This method fetches the referenced element and accesses the specified attribute via $element->$attribute.

• Missing Auth Check: It bypasses canView() checks.
• Polymorphic Access: getElementTypeByRefHandle allows referencing any element type (entry, asset, user, category).
• Custom Field Access: Since Craft elements use __get() to resolve custom field handles, an attacker is not limited to core attributes. They can exfiltrate any custom field data by enumerating the field handle (e.g. {entry:123:privateNotes}).

Attack Vectors

1. Privilege Escalation / User Data Leak

An attacker can enumerate sensitive attributes of administrators or other users.

• Payload: {user:1:email} or {user:1:photoId}

2. Arbitrary Property Reflection & Server-Side Logic Execution

The vulnerability allows reflecting any accessible property of the underlying Element model.

• Username/Admin Enumeration: {user:1:username} (Confirmed: returns admin), {user:1:admin}.
• Internal Path Disclosure: Accessing methods that trigger errors (e.g., {user:1:authKey}) exposes full server stack traces in the GraphQL error response (e.g., Exception: No user session token exists with paths like /var/www/html/...).

3. IDOR on Private Entries & Assets (Polymorphism)

The vulnerability is not limited to Users. Reference tags can target any element type.

• Payload: {entry:456:myConfidentialField} (Bypasses canView checks).
• Asset Path Leakage: {volume:1:path} can expose internal file system paths.

4. Unauthenticated Exploitation (Public Schema)

Confirmed locally. The @parseRefs directive is active in the Public Schema. By injecting a payload into a public-facing field (e.g., a "News" entry title), an unauthenticated guest can trigger the resolution and retrieve the sensitive output.

Steps to Reproduce

1. Setup (Admin Panel):

• Create a Section (e.g., "News") and an Entry Type.
• Create a new Entry in that section. Set the Title to the payload: {user:1:username} or {user:1:email}.
• Go to GraphQL > Schemas > Public Schema. Enable it, and ensure "Query for elements in the Site" and "News" section queries are checked.

2. Execute Exploit (Unauthenticated):

• Send a POST request to http://localhost:8000/index.php?action=graphql/api:

curl -X POST \
-H "Content-Type: application/json" \
-d '{"query": "{ entries { title @parseRefs } }"}'

3. Observation:

• The API returns {"data":{"entries":[{"title":"admin"}]}} (or the email).
• Using {user:1:authKey} triggers an internal server error that leaks the full server path in string format.

Impact

• Critical Information Disclosure: Full PII enumeration (emails, usernames).
• System Information Leakage: Absolute server paths via stack traces.
• Authentication Bypass: Guest accounts can effectively query the database as the system user.

Recommended Fix

Modify Elements::parseRefs to enforce canView permissions on the resolved element before extracting attributes.

References

https://github.com/craftcms/cms/commit/4d98a07e47580f1712095825d3e3c4d67bc9f8b9