Description

The Ninja Forms WordPress plugin 3.15.3 does not prevent user-submitted form field values from being deserialised when an administrator later exports form submissions to CSV, allowing unauthenticated attackers to perform PHP Object Injection; if a suitable POP chain is present via another installed plugin or theme, this can lead to actions such as arbitrary file operations or remote code execution.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.5",
  "pubDate": "2026-09-22T07:16:31.093Z",
  "pubdate": "2026-09-22T07:16:31.093Z",
  "executiveSummary": "The Ninja Forms WordPress plugin version 3.15.3 contains a critical security vulnerability involving insecure deserialization of user-supplied data.\nThe vulnerability occurs when an administrator initiates a CSV export of form submissions, triggering the deserialization of stored field values.\nThis flaw allows unauthenticated remote attackers to inject malicious serialized objects into form fields. If a viable POP (Property-Oriented Programming) chain exists within the application's environment—such as those found in other plugins or themes—the attacker can achieve arbitrary file operations or remote code execution (RCE).\nThe impact is severe, potentially resulting in full system compromise. The primary risk factor is the decoupling of the attack submission from the administrative action, as the exploit executes only when an administrator processes the form data. Organizations utilizing this version are at significant risk of privilege escalation and server-side compromise.",
  "technicalDetails": "The root cause of this vulnerability lies in the improper handling of user-submitted data within the Ninja Forms submission export functionality. Specifically, the plugin takes serialized data stored within the database and passes it to an unsafe deserialization function without performing adequate sanitization or structural validation.\nThe attack flow initiates when an unauthenticated attacker submits malicious serialized PHP objects through a public-facing form field. Because the plugin does not enforce strict input validation, these serialized strings are persisted directly into the WordPress database as legitimate form submission values. The vulnerability remains dormant until an administrator attempts to generate a CSV export of these submissions. During the export process, the application attempts to unserialize the stored data to process it for the CSV format. This triggers the PHP __wakeup() or __destruct() magic methods defined within classes available in the current application context.\nExploitation relies on the existence of a POP chain within the target WordPress environment. A POP chain is a sequence of existing class methods ('gadgets') that, when triggered via deserialization, can be orchestrated to perform unintended actions. If the application environment includes plugins or themes containing vulnerable classes, an attacker can craft a payload that chains these gadgets to achieve arbitrary file reads, file writes, or the execution of arbitrary PHP code.\nThe vulnerability is characterized by its delayed execution pattern. Since the attacker's input is stored and only executed upon an administrator-led administrative action, it effectively bypasses standard perimeter defenses that monitor for real-time web traffic threats. This necessitates high-level access to the database to persist the payload and requires the administrator to interact with the malicious submission, which is an inherent part of routine data management. The attack exposure is broad, as it affects any instance running version 3.15.3, with no authentication required to inject the initial serialized object. Successful exploitation grants the attacker the same system-level privileges as the PHP process owner, facilitating post-exploitation activities such as installing web shells, lateral movement, or complete exfiltration of site configuration data."
}