CVE-2026-66583 in Forminator Plugin
Summary
by MITRE • 08/20/2026
Unauthenticated PHP Object Injection in Forminator <= 1.57.0 versions.
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Analysis
by VulDB Data Team • 08/20/2026
The vulnerability identified as an unauthenticated PHP object injection flaw within the WordPress plugin Forminator, specifically affecting versions up to and including 1.57.0, represents a critical security risk that allows attackers to execute arbitrary code on vulnerable servers without requiring any form of user authentication or prior interaction with legitimate site users. This type of vulnerability stems from the improper handling of serialized data inputs where the application fails to validate or sanitize objects before passing them into functions capable of instantiating PHP classes, thereby enabling an attacker to manipulate the internal state of the application through crafted payloads that exploit magic methods such as __wakeup, __destruct, or __toString. The presence of this flaw indicates a fundamental misunderstanding of how PHP handles object serialization and deserialization processes, particularly when user-supplied data is directly utilized in these operations without sufficient safeguards against malicious class instantiation.
From a technical perspective, the core issue lies in the application's reliance on unserialize() or similar functions to process input parameters that are not adequately filtered for potentially dangerous classes. In many WordPress plugins, including Forminator, various features such as form submissions, file uploads, and data exports may accept user-controlled inputs which are then processed internally. If these inputs contain serialized PHP objects crafted by an attacker, the application's execution flow can be hijacked to instantiate arbitrary classes with controlled properties. This capability is particularly dangerous because it allows for remote code execution if a suitable gadget chain exists within the WordPress core or other installed plugins that interact with Forminator. The lack of authentication requirement means that any internet-facing website running this vulnerable version is immediately exposed, as no login credentials are needed to trigger the exploit, significantly lowering the barrier to entry for malicious actors and increasing the likelihood of automated attacks targeting known vulnerabilities in widely used software components.
The operational impact of this vulnerability extends beyond simple remote code execution; it compromises the integrity, confidentiality, and availability of the affected web application and its underlying infrastructure. An attacker who successfully exploits this flaw can gain full control over the server environment hosting the WordPress site, leading to potential data breaches involving sensitive user information stored in the database, such as personal details submitted through forms or administrative credentials. Furthermore, the compromised system may be used as a pivot point for further attacks against internal networks, distributed denial-of-service botnets, or malware distribution platforms. The ability to inject arbitrary code also allows attackers to modify website content, deface pages, or install backdoors that persist even after initial remediation efforts if not thoroughly audited and cleaned from the file system and database.
To mitigate this risk, immediate action is required by updating Forminator to version 1.57.1 or later, where the developers have implemented proper input validation and restricted the classes allowed during deserialization processes. Administrators should also review server configurations to ensure that PHP error reporting does not expose sensitive stack traces in production environments, as this information can aid attackers in crafting more effective exploits. Implementing a Web Application Firewall with rules specifically designed to detect serialized object injection patterns can provide an additional layer of defense while updates are being applied. Additionally, organizations should conduct thorough code audits focusing on all instances where unserialize() is used and replace them with safer alternatives or implement strict allowlists for permitted classes. Regular monitoring of security advisories from the WordPress plugin repository and maintaining up-to-date software dependencies are essential practices to prevent recurrence of such vulnerabilities in the future.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-502, which describes Deserialization of Untrusted Data, a category of flaws where applications fail to validate data before deserializing it, leading to potential remote code execution or other severe impacts. In terms of attack tactics and techniques, this exploitation vector corresponds to MITRE ATT&CK technique T1059, specifically Command and Scripting Interpreter sub-techniques such as T1059.004 for PowerShell or T1059.007 for JavaScript, depending on the specific payload used within the gadget chain. Understanding these mappings helps security teams prioritize remediation efforts based on standardized frameworks that reflect real-world adversary behaviors and common exploitation patterns observed in modern web application attacks.