CVE-2026-87067 in Forminator Forms Plugin
Summary
by MITRE • 09/20/2026
The Forminator Forms WordPress plugin before 1.57.2.1 does not restrict which classes may be instantiated when it deserialises a value taken from an XML-RPC request, allowing users who hold its forms-management permission to write a file of their choosing and execute arbitrary code. That permission belongs to an administrator by default, and to any role the site has granted it through the Forminator Forms WordPress plugin before 1.57.2.1's own settings, so the issue is reachable well below administrator on sites that use that feature.
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Analysis
by VulDB Data Team • 09/20/2026
The vulnerability identified in Forminator Forms for WordPress prior to version 1.57.2.1 represents a critical security flaw rooted in insecure deserialization practices within the plugin’s XML-RPC handling mechanism. Specifically, the application fails to implement strict class whitelisting or type checking when processing serialized data received via XML-RPC requests. This lack of restriction allows an attacker to supply crafted payloads that instruct PHP to instantiate arbitrary classes rather than only those intended by the developer. In modern web applications and CMS ecosystems like WordPress, deserializing untrusted input without rigorous validation is a well-documented anti-pattern that frequently leads to severe security breaches because serialized objects can contain methods or properties that trigger side effects during their reconstruction in memory.
The operational impact of this flaw is significant due to the specific permissions required to exploit it and the resulting capabilities granted to an attacker. The vulnerability requires the user to possess forms-management permission, which by default is assigned to administrators but can be delegated to lower-privileged roles through Forminator’s own configuration settings. This means that on sites where editors or contributors have been granted form management rights, they are effectively at risk of exploitation without needing full administrative access. Once exploited, an attacker can leverage the insecure deserialization to write files to arbitrary locations on the server filesystem and execute arbitrary code. This capability essentially allows for complete system compromise, as the web server process typically runs with permissions that allow writing to public directories or executing scripts within those directories, leading to remote code execution (RCE).
From a classification perspective, this vulnerability aligns closely with CWE-502, which describes Deserialization of Untrusted Data. The failure to validate and restrict the classes available for instantiation during the deserialization process is the core technical deficiency. Furthermore, in terms of offensive security frameworks such as MITRE ATT&CK, this exploit path relates to techniques involving Command Line Interface execution or File and Directory Information Discovery followed by Remote Code Execution. Attackers can use this flaw to establish persistence, escalate privileges if additional misconfigurations exist, or pivot further into the network depending on the server environment’s exposure and configuration.
Mitigation strategies must prioritize immediate remediation through software updates. Site administrators should upgrade Forminator Forms to version 1.57.2.1 or later, where this deserialization flaw has been addressed by implementing proper class whitelisting mechanisms that ensure only safe, expected classes are instantiated during XML-RPC processing. In environments where upgrading is not immediately feasible, temporary mitigations include restricting access to the XML-RPC endpoint if it is not actively required for legitimate functionality, or enforcing strict role-based access controls to ensure that forms-management permissions are granted only to trusted users with high levels of integrity. Additionally, implementing a Web Application Firewall (WAF) rule set capable of detecting anomalous serialized payloads in HTTP requests can provide an additional layer of defense against exploitation attempts while the underlying code is being patched.