Security Alert Summary
The Ninja Forms WordPress plugin version 3.15.3 does not prevent user-submitted form field values from being deserialised when an administrator later exports form submissions to CSV. This allows unauthenticated attackers to perform PHP Object Injection; if a suitable POP chain exists in another plugin or theme, the issue can enable actions such as arbitrary file operations or remote code execution.
CVE Details
- CVE ID: CVE-2026-91827
- Affected component: Ninja Forms WordPress plugin
- Affected versions: 3.15.3 (affected; versions less than 3.15.4)
- Published: September 22, 2026 at 7:16:31 AM UTC
- Last modified: September 22, 2026 at 11:17:26 AM UTC
- CVSS v3.1: Base score 7.5, severity HIGH,
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H - Authentication / privileges / user interaction: No authentication required (PR:N); user interaction is required (UI:R) for the exploit to be triggered in practice (an administrator must export submissions).
- Primary impact: Confidentiality: High; Integrity: High; Availability: High
- CWE / weakness: CWE-502 (Deserialization of Untrusted Data)
Technical Details
The plugin fails to prevent user-supplied form field values from being deserialised during the CSV export of form submissions. Specifically, when form data is exported by an administrator, the export process may deserialize stored values that originated from unauthenticated form submissions. This allows PHP Object Injection if an attacker can supply crafted serialized data.
The vulnerability relies on the presence of a suitable POP (Property Oriented Programming) chain in another installed plugin or theme to turn the deserialization into actionable impacts. Where such a chain exists, the injected object graph can lead to file operations or remote code execution. The CVE description identifies the root cause as unvalidated deserialization during the export workflow; no specific functions or REST endpoints are named in the provided data.
The impact is contextual: the deserialization vector provides a path to high-impact outcomes, but exploitation requires both the initial user-submitted payload and the administrative action of exporting submissions, and may require additional gadget chains from other code on the site.
How This Could Impact Your Website
Consider a site with multiple WordPress users: a site owner, internal staff who manage content, and external contributors or contractors who submit forms. An external attacker could submit specially crafted data through a public form (no authentication). If an administrator later exports submission data, the deserialization step could be abused to trigger PHP Object Injection. In environments where another plugin or theme provides a usable POP chain, this could allow attackers to perform arbitrary file operations or achieve remote code execution, potentially exposing or altering sensitive data.
Practical consequences include exposure of internal user information (for example, email addresses collected through forms) and increased risk of targeted phishing or social engineering against staff and contributors. The attack path depends on both the exported data and other code present on the site; it does not automatically imply full site compromise in every environment.
If youre unsure whether your site is affected or how to assess your current user roles and plugins, it may be worth having a professional review.
Recommended Actions
- Update the affected plugin as soon as a patched version is available.
- Review and reduce unnecessary user roles, especially contributor-level or anonymous submission privileges where possible.
- Enforce strong passwords and two-factor authentication for editors and administrators.
- Remove unused or unmaintained plugins and themes that could provide gadget chains.
- Monitor site activity and logs for unusual behavior, particularly around form submissions and export actions.
If youd like help reviewing your plugins, user roles, or overall WordPress security posture, our team at Freshy is happy to help.
