CVE-2025-26560: WP Contact Form III XSS Vulnerability

CVE-2025-26560 Overview

CVE-2025-26560 is a Reflected Cross-Site Scripting (XSS) vulnerability affecting the WP Contact Form III WordPress plugin developed by KKWangen. This vulnerability arises from improper neutralization of user-supplied input during web page generation, allowing attackers to inject malicious scripts that execute in the context of a victim's browser session.

Reflected XSS vulnerabilities in WordPress plugins pose significant risks to website administrators and visitors, as successful exploitation can lead to session hijacking, credential theft, defacement, and malware distribution through trusted websites.

Critical Impact

Attackers can execute arbitrary JavaScript code in the browsers of authenticated WordPress administrators, potentially leading to full site compromise through session hijacking or administrative action manipulation.

Affected Products

• WP Contact Form III WordPress Plugin versions up to and including 1.6.2d
• WordPress installations utilizing the vulnerable plugin versions
• Any website visitors or administrators accessing pages with the vulnerable plugin

Discovery Timeline

• 2025-03-26 - CVE-2025-26560 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-26560

Vulnerability Analysis

This vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation). The WP Contact Form III plugin fails to properly sanitize and escape user-controlled input before reflecting it back in the HTTP response. When malicious input containing JavaScript code is submitted through vulnerable parameters, the plugin echoes this input directly into the page without adequate encoding, causing the browser to execute the injected script.

The reflected nature of this XSS means the payload is not stored on the server but is instead delivered through a maliciously crafted URL. Attackers typically distribute these URLs through phishing emails, social media, or other channels to trick victims into clicking them.

Root Cause

The root cause of this vulnerability lies in insufficient input validation and output encoding within the WP Contact Form III plugin. The plugin processes user-supplied data and incorporates it into the HTML response without applying proper sanitization functions such as esc_html(), esc_attr(), or wp_kses() that WordPress provides for preventing XSS attacks.

WordPress plugins handling form data are particularly susceptible to XSS when developers fail to follow the WordPress security best practices for escaping output contextually based on where the data is rendered (HTML body, attributes, JavaScript, or URLs).

Attack Vector

The attack is executed remotely through the network without requiring any authentication or user privileges on the target WordPress site. An attacker crafts a malicious URL containing JavaScript payload within vulnerable parameters of the WP Contact Form III plugin. When a victim, particularly a WordPress administrator, clicks the link while authenticated, the malicious script executes with their session privileges.

A typical attack scenario involves:

1. The attacker identifies a vulnerable installation of WP Contact Form III
2. The attacker crafts a URL with embedded JavaScript payload targeting vulnerable parameters
3. The malicious URL is distributed to potential victims through phishing or social engineering
4. When clicked by an authenticated user, the script executes in their browser context
5. The attacker can then steal session cookies, perform actions on behalf of the user, or redirect to malicious sites

For detailed technical analysis of this vulnerability, refer to the Patchstack vulnerability database entry.

Detection Methods for CVE-2025-26560

Indicators of Compromise

• Suspicious URLs containing encoded JavaScript payloads targeting WP Contact Form III parameters
• Web access logs showing requests with unusual characters or script tags in query strings
• Browser console errors indicating blocked or executed inline scripts
• Unexpected redirects or behavior when accessing contact form pages

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block common XSS patterns in request parameters
• Monitor server access logs for requests containing <script>, javascript:, onerror=, and other XSS indicators
• Deploy Content Security Policy (CSP) headers to prevent inline script execution and report violations
• Use browser-based XSS auditors and security extensions that can detect reflected content

Monitoring Recommendations

• Enable WordPress security audit logging to track plugin-related activities
• Configure real-time alerting for suspicious request patterns targeting form endpoints
• Review CSP violation reports for attempted XSS injections
• Regularly scan the WordPress installation with security plugins that check for known vulnerable plugin versions

How to Mitigate CVE-2025-26560

Immediate Actions Required

• Deactivate and remove the WP Contact Form III plugin (wp-contact-form-iii) if running version 1.6.2d or earlier
• Review WordPress site for any signs of compromise or unauthorized administrative changes
• Clear browser caches and reset sessions for WordPress administrators who may have been exposed
• Consider implementing a Web Application Firewall with XSS protection rules

Patch Information

As of the CVE publication, all versions of WP Contact Form III through 1.6.2d are affected by this vulnerability. Website administrators should check the Patchstack advisory for updates on patched versions or consider migrating to an alternative contact form plugin with active security maintenance.

Workarounds

• Disable the WP Contact Form III plugin until a patched version is available
• Implement server-side input filtering to strip potentially malicious characters from form submissions
• Deploy Content Security Policy headers to mitigate XSS impact: Content-Security-Policy: default-src 'self'; script-src 'self'
• Use a Web Application Firewall with rules specifically designed to block reflected XSS attempts

# Add CSP headers in Apache .htaccess
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none'"

# Or in nginx configuration
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none'" always;