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GHSA-86vw-x4ww-x467
No affected components available
The actionRenderCardPreview() method in FieldsController passes the fieldLayoutConfig POST parameter directly to Fields::createLayout() without calling Component::cleanseConfig(). This allows Yii2 event handler injection via on eventName keys in the config array, leading to arbitrary code execution.
This is the same vulnerability pattern that was fixed in GHSA-4484-8v2f-5748 (same file, _fldComponent method correctly uses cleanseConfig), GHSA-qx2q-q59v-wf3j (EntryTypesController), and GHSA-2fph-6v5w-89hh (ElementIndexesController).
PoC
As an admin user with a valid session:
POST /admin/actions/fields/render-card-preview HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Cookie: CraftSessionId=<session>
fieldLayoutConfig[on+init]=phpinfo&CRAFT_CSRF_TOKEN=<token>
When the FieldLayout object is constructed, Yii2 processes the on init key as an event handler registration. During Component::init(), the init event is triggered, calling phpinfo(). The phpinfo output (which includes environment variables, potentially containing database credentials and CRAFT_SECURITY_KEY) will appear in the response.
Impact
An authenticated admin can achieve RCE through Yii2 event handler injection. While this requires admin access (same as GHSA-4484-8v2f-5748, which was rated moderate), it allows arbitrary PHP function execution and information disclosure via phpinfo.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs high-level or administrative privileges. No user interaction is needed for the attacker to exploit this vulnerability.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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