Overview
In this blog post, we delve into a critical cybersecurity vulnerability, CVE-2025-9083, which affects users of the popular Ninja Forms WordPress plugin. This vulnerability, if exploited, could allow unauthenticated users to perform a PHP Object Injection attack on a blog where a suitable gadget is present. Given the vast number of websites that use WordPress and Ninja Forms, this vulnerability presents a significant security risk, which could potentially lead to system compromise or data leakage.
Vulnerability Summary
CVE ID: CVE-2025-9083
Severity: Critical (9.8 CVSS Score)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: System compromise or data leakage
Affected Products
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Product | Affected Versions
Ninja Forms WordPress plugin | Before 3.11.1
How the Exploit Works
The Ninja Forms plugin before 3.11.1 unserializes user input via form fields. An attacker could exploit this vulnerability by sending a malicious object through the form field, which is then unserialized by the plugin. This could allow the attacker to execute arbitrary code on the server hosting the website – a PHP Object Injection attack. Since no authentication is required, any unauthenticated user could potentially exploit this vulnerability.
Conceptual Example Code
Here’s a conceptual example of how the vulnerability might be exploited. In this example, a malicious HTTP POST request is sent to a vulnerable endpoint:
POST /wp-content/plugins/ninja-forms/submit.php HTTP/1.1
Host: target.example.com
Content-Type: application/json
{ "form_fields": {"object": "base64_encoded_malicious_object"} }In this hypothetical attack, the `base64_encoded_malicious_object` would be a Base64-encoded serialized PHP object designed to perform malicious actions when unserialized.
Mitigation Guidance
To prevent potential exploitation of this vulnerability, it is recommended to apply the vendor’s patch by updating the Ninja Forms plugin to version 3.11.1 or later. If patching is not immediately possible, the use of a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can provide temporary mitigation. These systems should be configured to block or alert on suspicious payloads sent to endpoints associated with the Ninja Forms plugin. Regularly updating all plugins and applications, and monitoring for the release of security patches, is a fundamental part of maintaining a secure web presence.
