CVE-2026-101326 in Ninja Forms Plugin
Summary
by MITRE • 10/31/2026
The The Ninja Forms – Contact Form Builder with Calculators, Quizzes, Signatures & AI Form Builder plugin for WordPress is vulnerable to arbitrary shortcode execution in all versions up to, and including, 3.15.5 This is due to the software allowing users to execute an action that does not properly validate a value before running do_shortcode. This makes it possible for authenticated attackers, with subscriber-level access and above, to execute arbitrary shortcodes. Exploitation requires that an administrator has configured at least one Ninja Forms field with its Default Value set to the {wp:user_display_name} merge tag on a publicly accessible page; a Subscriber need only set their display_name to a shortcode string via their profile and then visit that page.
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Analysis
by VulDB Data Team • 10/31/2026
The vulnerability identified in The Ninja Forms plugin for WordPress, affecting versions up through 3.15.5, represents a critical security flaw classified as Arbitrary Shortcode Execution. This issue stems from an improper validation mechanism within the software's handling of user-provided data during the rendering process. Specifically, the application fails to adequately sanitize or validate values before passing them into the WordPress core function do_shortcode. This architectural oversight allows for the injection and subsequent execution of malicious shortcode payloads by authenticated users who possess subscriber-level access or higher privileges. The severity of this vulnerability is amplified by its potential impact on site integrity and data confidentiality, as shortcodes in WordPress are powerful constructs capable of executing complex PHP code, accessing database information, and interacting with server-side resources when not properly constrained.
From a technical perspective, the exploitation vector relies heavily on social engineering combined with specific configuration states within the target environment. The attacker must first register an account or utilize existing credentials at subscriber level or above to modify their profile settings. By setting their display_name field to contain a malicious shortcode string, such as one that triggers file inclusion or data exfiltration functions, the user creates a payload stored in the database. When this information is later retrieved and processed by Ninja Forms, it bypasses expected security boundaries because the plugin treats the merge tag content as executable code rather than plain text. The critical precondition for successful exploitation involves an administrator having previously configured at least one form field with its Default Value set to the {wp:user_display_name} merge tag on a publicly accessible page. This configuration creates a direct pipeline from user input to shortcode execution without intermediate sanitization steps, effectively turning standard profile data into a vehicle for code injection.
The operational impact of this vulnerability is significant, particularly in multi-user environments where low-privilege accounts are common. An attacker with subscriber-level access can achieve remote code execution capabilities indirectly by leveraging the server's own rendering engine to process arbitrary shortcodes. This could lead to unauthorized access to sensitive data stored within WordPress databases, such as user credentials or form submissions containing personal identifiable information. Furthermore, depending on the specific shortcode executed, an attacker might be able to escalate privileges, deface websites, install backdoors for persistent access, or disrupt service availability through resource exhaustion attacks triggered by malicious shortcodes. The fact that exploitation requires only subscriber-level access makes this vulnerability particularly dangerous in public-facing sites where registration is open to untrusted users.
This flaw aligns with CWE-94 Improper Control of Generation of Code (Code Injection) and specifically relates to the injection of executable content through insufficient validation of input data before processing. In terms of offensive security frameworks, it maps to MITRE ATT&CK techniques involving Command and Scripting Interpreter abuse, where attackers leverage legitimate system functions for malicious purposes. The vulnerability also touches upon CWE-601 URL Redirection to Untrusted Site (Open Redirect) if the shortcodes are used to manipulate redirects, though its primary classification remains code injection via input validation failure.
Mitigation strategies must address both immediate remediation and long-term defensive posture improvements. Administrators should immediately update The Ninja Forms plugin to version 3.15.6 or later, where this issue has been resolved through enhanced input sanitization and output escaping mechanisms. For sites unable to patch immediately due to compatibility concerns, disabling the {wp:user_display_name} merge tag in publicly accessible forms is a viable temporary workaround. Additionally, implementing strict Content Security Policy headers can help mitigate some effects of script injection, although it does not prevent server-side shortcode execution. Organizations should also enforce principle of least privilege by reviewing user roles and ensuring that only trusted individuals have access to form configuration settings. Regular security audits focusing on how third-party plugins handle dynamic content insertion are essential for maintaining a robust WordPress ecosystem against similar input validation flaws.