WordPress Ninja Forms Plugin Arbitrary Shortcode Execution Vulnerability (CVE-2026-101326)

1. Apply Official Patch

The recommended remediation is to upgrade the Ninja Forms plugin to the latest secure version (3.15.6 or higher). You can update via the WordPress admin dashboard or use WP-CLI:

# Update plugin using WP-CLI
wp plugin update ninja-forms

2. Temporary Mitigation (If patching is delayed)

If immediate patching is not feasible, apply the following workarounds to mitigate the risk:

• Modify Form Configurations: Inspect all active and public Ninja Forms. Ensure that no form fields have their 'Default Value' set to the {wp:user_display_name} merge tag.
• Restrict Profile Updates: Monitor or restrict the ability of low-privileged users (Subscribers) to change their display names to strings containing square brackets ([ and ]).

This is an arbitrary shortcode execution vulnerability (CWE-94) in the Ninja Forms plugin for WordPress, stemming from insufficient input validation before executing a core WordPress rendering function.

Root Cause & Exploit Mechanics

• Lack of Validation: The plugin allows the execution of an action that runs the do_shortcode() function without properly validating or sanitizing the input value beforehand.
• Merge Tag Exploitation: The vulnerability is exploitable if an administrator has configured at least one Ninja Forms field on a publicly accessible page with its Default Value set to the {wp:user_display_name} merge tag.
• Attack Vector: An authenticated attacker with low-privileged Subscriber access can update their profile's display_name to a malicious shortcode string. When the attacker visits the page containing the configured form, the plugin processes the {wp:user_display_name} merge tag and executes the injected shortcode via do_shortcode(), leading to unauthorized information disclosure or functional abuse.