CVE-2026-78363: MW WP Form WordPress Plugin XSS Vulnerability

CVE-2026-78363 Overview

CVE-2026-78363 is a shortcode injection vulnerability in the MW WP Form WordPress plugin affecting versions prior to 5.1.5. The plugin fails to sanitize user-submitted values before merging them into a message that is later processed for shortcodes. Unauthenticated attackers can inject and execute any shortcode registered on the target site. Exploitation requires the site to echo a submitted value back to the visitor after form submission. The flaw is classified under [CWE-74] (Improper Neutralization of Special Elements in Output).

Critical Impact
Unauthenticated attackers can execute arbitrary registered shortcodes on affected WordPress sites, potentially exposing site data or triggering plugin functionality intended for authorized users.

Affected Products

MW WP Form WordPress plugin versions prior to 5.1.5
WordPress sites configured to echo submitted form values back to visitors
Any site where MW WP Form processes shortcodes in submitted content

Discovery Timeline

2026-09-01 - CVE-2026-78363 published to NVD
2026-09-01 - Last updated in NVD database

Technical Details for CVE-2026-78363

Vulnerability Analysis

The MW WP Form plugin processes form submissions and provides an option to display submitted values back to the user in a confirmation or response message. When the plugin merges user-controlled values into that message, it runs WordPress shortcode processing on the resulting content. Because user input is not stripped of shortcode syntax before this merge, attackers can submit values containing shortcodes that the site later renders.

Exploitation depends on the site's form configuration. The administrator must configure the form to echo one or more submitted fields back to the visitor. Once that condition is met, any unauthenticated visitor can submit a form and receive a rendered response containing the output of arbitrary shortcodes registered on the site.

The impact varies by which shortcodes exist on the target site. Shortcodes that expose sensitive content, invoke administrative helpers, or return user or system data become reachable to anonymous attackers through the form response.

Root Cause

The root cause is improper neutralization of shortcode delimiters in user-controlled input. The plugin trusts submitted values during message assembly and then applies do_shortcode() semantics to the assembled string. This mixes untrusted input with a code-execution primitive tied to the WordPress shortcode API.

Attack Vector

The attack is network-based and requires no authentication or user interaction from a victim. Attack complexity is high because exploitation depends on a specific site configuration that echoes user input back after submission. Attackers craft form field values containing shortcode syntax and submit them through the public-facing form endpoint. The plugin merges these values into its response message and processes them as shortcodes.

A public proof-of-concept is not listed in the enriched data. Technical details are documented in the WPScan Vulnerability Report.

Detection Methods for CVE-2026-78363

Indicators of Compromise

Form submissions containing shortcode delimiters such as [ and ] inside user-input fields
Web server access logs showing POST requests to MW WP Form endpoints with shortcode syntax in payloads
Unexpected content in form confirmation responses that matches output of registered site shortcodes
Outbound requests or data exposure originating from shortcode handlers immediately after public form submissions

Detection Strategies

Inspect HTTP request bodies to MW WP Form endpoints for shortcode patterns matching the regex \[[a-zA-Z0-9_\-]+
Review installed plugin versions across managed WordPress sites and flag MW WP Form releases below 5.1.5
Correlate form submission events with shortcode execution in response bodies to identify successful injection attempts

Monitoring Recommendations

Enable WordPress audit logging for plugin activity and form submissions
Monitor web application firewall (WAF) alerts for shortcode-like payloads submitted to public forms
Track anomalous response sizes or content from MW WP Form confirmation pages that may indicate rendered shortcode output

How to Mitigate CVE-2026-78363

Immediate Actions Required

Update the MW WP Form plugin to version 5.1.5 or later on all WordPress installations
Audit form configurations and remove echo-back of submitted values where not strictly required
Review the list of shortcodes registered on affected sites and disable any that expose sensitive data or privileged actions

Patch Information

The vendor has released MW WP Form version 5.1.5, which addresses the shortcode injection flaw. Site administrators should apply the update through the WordPress plugin manager or by installing the patched release manually. Refer to the WPScan Vulnerability Report for advisory details.

Workarounds

Reconfigure affected forms to remove any confirmation message that echoes submitted values back to the visitor
Deploy WAF rules that block or strip shortcode syntax from MW WP Form submission payloads
Restrict access to public forms using IP allowlisting or CAPTCHA until the plugin is patched

bash

# Update MW WP Form via WP-CLI
wp plugin update mw-wp-form --version=5.1.5
wp plugin list --name=mw-wp-form --fields=name,status,version