CVE-2026-4394: Gravity Forms WordPress Plugin XSS Flaw

CVE-2026-4394 Overview

The Gravity Forms plugin for WordPress is vulnerable to Stored Cross-Site Scripting (XSS) via the Credit Card field's 'Card Type' sub-field (input_<id>.4) in all versions up to, and including, 2.9.30. This vulnerability arises from improper input sanitization and output encoding within the GF_Field_CreditCard class. Specifically, the get_value_entry_detail() method outputs the card type value without proper escaping, while get_value_save_entry() accepts and stores unsanitized user input for the input_<id>.4 parameter.

What makes this vulnerability particularly insidious is that the Card Type field is not rendered on the frontend form—it is normally derived automatically from the card number. However, the backend submission parser blindly accepts this parameter if included in a crafted POST request, allowing unauthenticated attackers to inject arbitrary web scripts that execute when an administrator views the form entry in the WordPress dashboard.

Critical Impact

Unauthenticated attackers can inject malicious JavaScript that executes in the context of WordPress administrators, potentially leading to admin session hijacking, unauthorized configuration changes, or further compromise of the WordPress installation.

Affected Products

• Gravity Forms WordPress Plugin versions up to and including 2.9.30
• WordPress installations with vulnerable Gravity Forms versions configured with Credit Card fields
• Any WordPress site processing form submissions through affected Gravity Forms versions

Discovery Timeline

• 2026-04-08 - CVE-2026-4394 published to NVD
• 2026-04-08 - Last updated in NVD database

Technical Details for CVE-2026-4394

Vulnerability Analysis

This Stored Cross-Site Scripting vulnerability exploits a fundamental flaw in how the Gravity Forms plugin handles the Credit Card field's hidden sub-field. The vulnerability chain consists of two interconnected issues in the GF_Field_CreditCard class.

The first issue lies in the get_value_save_entry() method, which is responsible for processing and storing form submission data. This method accepts the input_<id>.4 parameter (Card Type) from POST requests without proper sanitization, even though this field should never be submitted by legitimate users since it's derived client-side from the card number.

The second issue occurs in the get_value_entry_detail() method, which retrieves and displays stored entry values in the WordPress admin dashboard. This method outputs the card type value without applying proper HTML escaping functions like esc_html() or wp_kses(), allowing stored malicious scripts to execute in the administrator's browser context.

Root Cause

The root cause is twofold: insufficient input validation combined with missing output encoding. The plugin fails to validate that the Card Type sub-field should only contain expected card type values (e.g., "Visa", "MasterCard") and does not sanitize the input before database storage. Additionally, when displaying the stored value, the plugin outputs raw user-controlled data without escaping, creating a classic Stored XSS condition.

The vulnerable code paths can be examined in the source code files on WordPress plugin repository. The get_value_save_entry() function at line 516 and get_value_entry_detail() at line 577 both contribute to this vulnerability.

Attack Vector

The attack exploits the trust boundary between frontend form rendering and backend submission processing. An attacker crafts a malicious POST request to a form endpoint, including a specially crafted input_<id>.4 parameter containing JavaScript payload. Since the backend parser does not validate the source of this field value, the malicious content is stored in the database. When an administrator navigates to view form entries in the WordPress dashboard, the unescaped malicious script executes in their authenticated browser session.

The vulnerability mechanism works as follows: An attacker identifies a WordPress site using Gravity Forms with a Credit Card field, crafts a POST request containing the form's standard fields plus the hidden Card Type sub-field with an XSS payload, submits the request which stores the malicious data, and waits for an administrator to view the form entry. For detailed technical analysis, see the Wordfence Vulnerability Report.

Detection Methods for CVE-2026-4394

Indicators of Compromise

• Unexpected or suspicious content in form entry data, particularly in Credit Card field entries containing script tags or JavaScript event handlers
• Anomalous POST requests to form submission endpoints containing input_*.4 parameters with HTML or script content
• Administrator reports of unexpected browser behavior or pop-ups when viewing Gravity Forms entries
• Web application firewall logs showing blocked XSS payloads targeting form submission endpoints

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block XSS payloads in POST parameters, particularly targeting input_*.4 parameter patterns
• Enable WordPress audit logging to monitor form submission activities and admin dashboard access patterns
• Review database entries in the Gravity Forms tables for suspicious content containing <script>, javascript:, onerror, or similar XSS vectors
• Deploy Content Security Policy (CSP) headers to mitigate successful exploitation impact

Monitoring Recommendations

• Monitor HTTP POST requests to Gravity Forms submission endpoints for unusual parameters or payloads
• Implement real-time alerting for XSS pattern matches in form submission data
• Track administrator session activity for signs of session hijacking or unauthorized actions following form entry views
• Regularly audit stored form entries for potentially malicious content

How to Mitigate CVE-2026-4394

Immediate Actions Required

• Update Gravity Forms plugin to a version newer than 2.9.30 that includes the security fix
• Audit existing form entries for potentially malicious content that may have been stored prior to patching
• Implement additional WAF rules to block XSS payloads targeting Gravity Forms endpoints
• Review administrator accounts for any signs of compromise or unauthorized activity

Patch Information

The vulnerability affects Gravity Forms versions up to and including 2.9.30. Site administrators should update to the latest patched version immediately. Consult the Gravity Forms Change Log for information about security updates and the specific version containing the fix.

Workarounds

• If immediate updating is not possible, temporarily disable Credit Card fields in affected forms until the patch can be applied
• Implement strict WAF rules to sanitize or block POST requests containing suspicious content in input_*.4 parameters
• Restrict WordPress admin dashboard access to trusted IP addresses to limit exposure of stored XSS payloads
• Apply Content Security Policy headers with strict script-src directives to prevent inline script execution

# Example Apache configuration to add CSP headers
# Add to .htaccess or Apache configuration file
<IfModule mod_headers.c>
    Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline';"
</IfModule>