CVE-2025-23503: Customizable Captcha XSS Vulnerability

CVE-2025-23503 Overview

CVE-2025-23503 is a Reflected Cross-Site Scripting (XSS) vulnerability affecting the Customizable Captcha and Contact Us WordPress plugin developed by osolwordpress. This vulnerability allows attackers to inject malicious scripts into web pages viewed by other users by exploiting improper neutralization of input during web page generation.

Reflected XSS vulnerabilities in WordPress plugins are particularly concerning as they can be leveraged to steal session cookies, hijack user accounts, perform unauthorized actions on behalf of authenticated users, or redirect victims to malicious websites.

Critical Impact

Attackers can execute arbitrary JavaScript in the context of a victim's browser session, potentially leading to session hijacking, credential theft, or defacement of WordPress sites using this plugin.

Affected Products

• Customizable Captcha and Contact Us WordPress Plugin version 1.0.2 and earlier
• All WordPress installations using the vulnerable customizable-captcha-and-contact-us-form plugin

Discovery Timeline

• 2025-01-22 - CVE-2025-23503 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-23503

Vulnerability Analysis

This vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting. The Customizable Captcha and Contact Us plugin fails to properly sanitize user-supplied input before reflecting it back in the generated HTML output.

In a Reflected XSS attack scenario, an attacker crafts a malicious URL containing JavaScript code as part of a parameter value. When an unsuspecting user clicks this link, the malicious script is executed in their browser within the security context of the vulnerable WordPress site.

The plugin's contact form functionality appears to echo user input without adequate encoding or filtering, allowing specially crafted payloads to break out of the intended HTML context and execute arbitrary JavaScript code.

Root Cause

The root cause of this vulnerability stems from inadequate input validation and output encoding within the plugin's web page generation routines. The plugin fails to sanitize or properly encode user-controllable input before incorporating it into the HTML response, violating the fundamental security principle of treating all user input as potentially malicious.

WordPress provides built-in escaping functions such as esc_html(), esc_attr(), and wp_kses() that should be applied to all user-supplied data before output. The absence of these protective measures in the affected plugin versions allows XSS payloads to execute.

Attack Vector

The attack requires user interaction, as the victim must click a maliciously crafted link or visit a page controlled by the attacker that redirects to the vulnerable endpoint. The attacker constructs a URL containing a JavaScript payload in one of the plugin's parameters. When a WordPress administrator or authenticated user clicks this link, the malicious script executes with their privileges.

Typical attack scenarios include:

• Phishing emails containing malicious links to the vulnerable WordPress site
• Social engineering attacks through social media or forums
• Watering hole attacks where the malicious URL is embedded in a compromised third-party site

For technical details on exploitation and the specific vulnerable parameters, refer to the Patchstack WordPress Vulnerability Report.

Detection Methods for CVE-2025-23503

Indicators of Compromise

• Unusual JavaScript execution patterns in browser console logs from WordPress admin pages
• Suspicious URL parameters containing encoded script tags or event handlers in web server access logs
• Unexpected outbound connections from user browsers to unknown external domains
• Reports of unexpected behavior or pop-ups when interacting with the contact form

Detection Strategies

• Review web server access logs for requests containing common XSS payloads such as <script>, javascript:, onerror=, or onload= in URL parameters
• Implement Content Security Policy (CSP) headers to detect and block inline script execution attempts
• Deploy web application firewalls (WAF) with XSS detection rules to identify and block malicious requests
• Monitor for unusual DOM modifications or script injections using browser-based security extensions

Monitoring Recommendations

• Enable verbose logging for the WordPress site and analyze for suspicious parameter patterns
• Configure alerting for any requests containing URL-encoded special characters targeting plugin endpoints
• Implement real-time monitoring for client-side JavaScript errors that may indicate XSS exploitation attempts

How to Mitigate CVE-2025-23503

Immediate Actions Required

• Deactivate and remove the Customizable Captcha and Contact Us plugin immediately if running version 1.0.2 or earlier
• Review web server logs for evidence of exploitation attempts targeting this vulnerability
• Consider implementing a Web Application Firewall (WAF) rule to block requests containing XSS payloads
• Audit other installed WordPress plugins for similar input validation vulnerabilities

Patch Information

As of the publication date, no official patch has been released for this vulnerability. The affected versions include all releases through version 1.0.2. Site administrators should check the Patchstack WordPress Vulnerability Report for updates on patch availability.

Workarounds

• Remove the vulnerable plugin entirely and replace it with a well-maintained alternative captcha and contact form solution
• Implement server-side input filtering to strip potentially dangerous characters from all form inputs
• Deploy Content Security Policy headers to mitigate the impact of any XSS exploitation
• Use a WordPress security plugin that provides virtual patching capabilities for known vulnerabilities

# Add Content Security Policy headers to WordPress .htaccess
# This helps mitigate XSS attacks by restricting script execution

<IfModule mod_headers.c>
    Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline';"
    Header set X-XSS-Protection "1; mode=block"
    Header set X-Content-Type-Options "nosniff"
</IfModule>