CVE-2026-86732 in Craft CMS
Summary
by MITRE • 09/08/2026
Craft CMS versions before 5.10.12 contain a remote code execution vulnerability in the element-index endpoint that allows authenticated content editors to instantiate arbitrary classes through the criteria parameter. Attackers can inject a malicious class via criteria[withTransforms][0][class] that reaches ImageTransforms::normalizeTransform(), then use a PHP gadget chain with yii\rbac\PhpManager to execute code by pointing itemFile to a request log containing PHP payload in the User-Agent header.
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Analysis
by VulDB Data Team • 09/08/2026
Craft CMS versions prior to 5.10.12 contain a critical remote code execution vulnerability within the element-index endpoint, which allows authenticated content editors with sufficient privileges to instantiate arbitrary classes through manipulation of the criteria parameter. This flaw stems from insufficient validation and sanitization of user-supplied input when processing array-based parameters for image transformations. Specifically, an attacker can inject a malicious class name via the path criteria[withTransforms][0][class], which is then passed directly into ImageTransforms::normalizeTransform(). The function fails to restrict instantiation to expected classes within the Craft CMS framework or its approved extensions, thereby enabling arbitrary object creation that serves as the entry point for further exploitation.
The operational impact of this vulnerability is severe because it facilitates a PHP gadget chain attack leveraging the Yii2 framework's built-in functionality. Once an attacker successfully instantiates a controlled class through the aforementioned endpoint, they can manipulate properties to trigger deserialization or other dangerous side effects within dependent components. In this specific scenario, the exploitation path targets yii\rbac\PhpManager, a component responsible for managing role-based access control using PHP files. By setting the itemFile property of this manager instance to point toward a request log file that contains a malicious PHP payload embedded in the User-Agent header, an attacker can achieve arbitrary code execution when the framework attempts to read or process these items. This technique effectively bypasses traditional input validation by reusing existing application artifacts and configuration mechanisms as vectors for exploitation.
This vulnerability aligns with CWE-94 Improper Control of Generation of Code (Code Injection) due to the ability to inject executable logic through class instantiation, as well as CWE-502 Deserialization of Untrusted Data if interpreted broadly within the context of gadget chains leading to execution. From an ATT&CK perspective, this falls under T1059 Command and Scripting Interpreter via PHP, specifically leveraging local file inclusion or arbitrary code execution techniques enabled by framework-specific deserialization flaws. The attack requires authentication as a content editor, which limits the initial access vector but significantly increases the potential impact given that such roles often have broad permissions within CMS environments to manage media assets and site structure.
Mitigation strategies must prioritize immediate upgrading of Craft CMS to version 5.10.12 or later, where this input validation issue has been addressed by restricting class instantiation to a whitelist of safe classes. In the interim, administrators should enforce strict role-based access controls to limit who can interact with element-index endpoints and ensure that only trusted users have editor-level privileges. Additionally, implementing Web Application Firewall rules to detect anomalous patterns in array parameters related to image transformations or RBAC managers may provide partial protection against exploitation attempts. Regularly rotating log files and ensuring they are not stored in web-accessible directories further reduces the risk of successful gadget chain completion by removing the target payload location from easy reach for potential attackers who might have gained limited access through other means.