CVE-2026-96833 in Ultimate Addons for Contact Form 7 Plugin
Summary
by MITRE • 09/30/2026
Editor PHP Object Injection in Ultimate Addons for Contact Form 7 <= 3.5.51 versions.
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified as an Editor PHP Object Injection within the Ultimate Addons for Contact Form 7 plugin, affecting versions up to and including 3.5.51, represents a critical security flaw rooted in improper handling of user-supplied input during object serialization processes. This specific type of attack leverages the PHP language feature known as "unserialize," which converts serialized data back into its original PHP variable structure. When an application accepts untrusted data and passes it directly to unserialize without rigorous validation or sanitization, attackers can craft malicious payloads that result in arbitrary code execution, denial of service, or privilege escalation upon deserialization. In the context of this plugin, the flaw likely resides within a component responsible for rendering or processing form editor settings where user input is not adequately filtered before being processed by internal PHP functions that reconstruct objects from string representations.
From a technical perspective, this vulnerability aligns with CWE-502, which describes Deserialization of Untrusted Data. The core issue arises because the application fails to verify the integrity and origin of the serialized data stream. An attacker who has access to any input field managed by the Ultimate Addons for Contact Form 7 interface can inject a specially crafted PHP object string. When this payload is processed, it triggers unintended side effects within the PHP runtime environment. Depending on the available classes in the WordPress execution context and the specific configuration of the server, these side effects may include executing arbitrary system commands, accessing sensitive files such as wp-config.php to extract database credentials, or manipulating session data to hijack administrative accounts. The severity is exacerbated by the widespread adoption of Contact Form 7, which means that any site utilizing this plugin with vulnerable addon versions becomes a potential target for automated exploitation campaigns.
The operational impact of exploiting this vulnerability extends beyond simple defacement or temporary disruption. Successful exploitation allows an attacker to achieve Remote Code Execution (RCE) on the web server hosting the WordPress instance. This level of access effectively compromises the entire system, not just the application layer. Attackers can install persistent backdoors, deploy cryptomining scripts, exfiltrate customer data collected through forms, or use the compromised server as a pivot point for further network intrusion. For organizations relying on these contact forms for lead generation and communication, such an incident results in significant reputational damage, potential regulatory penalties under frameworks like GDPR due to data breach exposure, and substantial costs associated with forensic investigation and remediation efforts. The lack of immediate detection mechanisms means that the compromise may persist undetected for extended periods, allowing attackers to establish deep footholds within the infrastructure.
Mitigation strategies must address both the immediate technical flaw and broader security hygiene practices. The primary and most effective mitigation is to upgrade Ultimate Addons for Contact Form 7 to a version greater than 3.5.51 where this vulnerability has been patched by the developers through input validation and safe serialization handling techniques. If upgrading is not immediately feasible, administrators should consider disabling the specific addon features that trigger the vulnerable code path or restricting access to the WordPress admin area using strong authentication methods such as multi-factor authentication (MFA) and IP whitelisting for administrative users. Additionally, implementing a Web Application Firewall (WAF) can help detect and block common exploitation patterns associated with PHP object injection attempts by inspecting request payloads for known malicious signatures related to unserialize calls or suspicious class instantiations.
Long-term resilience against such vulnerabilities requires adherence to secure coding standards and continuous monitoring. Developers should avoid using native PHP serialization functions like serialize and unserialize on untrusted data, opting instead for safer alternatives like JSON encoding which does not support arbitrary object instantiation. Security teams should integrate static application security testing (SAST) tools into their development pipelines to identify deserialization flaws early in the lifecycle. Furthermore, maintaining an inventory of all installed plugins and regularly auditing them against known vulnerability databases ensures that organizations remain aware of emerging threats affecting their technology stack. By combining immediate patching with robust defensive controls and secure development practices, organizations can significantly reduce their attack surface and protect critical web applications from exploitation via PHP object injection vectors.