CVE-2025-23840 – Reflected XSS Vulnerability in WP-NOTCAPTCHA Plugin

Recently, an Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability has been discovered, also known as CVE-2025-23840. This vulnerability exists within the Webjema WP-NOTCAPTCHA plugin which is widely used by website developers for WordPress websites. WP-NOTCAPTCHA, ranging from version N/A through 1.3.1, is affected by this vulnerability known as Reflected XSS. In this detailed post, we'll go over the CVE-2025-23840 vulnerability, providing code snippets, links to original references, and exploit details.

Vulnerability Details

A Reflected XSS vulnerability occurs when a web application utilizes user-supplied data in the output reflected back to the user without proper validation. This can potentially allow an attacker to execute malicious scripts that can access sensitive user data, deface web content, or redirect users to malicious sites. In the case of the Webjema WP-NOTCAPTCHA plugin, this vulnerability exists due to improper handling and neutralization of input while generating the web page.

Affected Plugin: Webjema WP-NOTCAPTCHA

- Affected Versions: N/A through 1.3.1

The following code snippet demonstrates the vulnerable part within the Webjema WP-NOTCAPTCHA plugin

<?php
function wp_not_captcha_result( $atts ) {
    $a = shortcode_atts( array(
        'action' => 'notcaptcha_result',
        'id' => 'wp-notcaptcha-widget'
    ), $atts );

    $result = '<div id="' . $a['id'] . '">' . do_shortcode('[notcaptcha]') . '</div>';
    return $result;
}
?>

In this code, the 'id' value of the HTML 'div' element is initialized with the 'id' attribute provided from the user through the shortcode. The user input is not sanitized before being directly applied to the HTML output, allowing an attacker to perform a Reflected XSS attack.

For example, an attacker could create a malicious shortcode like this

[notcaptcha_result id="wp-notcaptcha-widget" onmouseover="alert(document.cookie)"]

When this malicious shortcode is placed in a post or page, the attacker can execute their XSS payload by simply hovering their cursor over the affected section.

Mitigation Steps

The easiest way to prevent the vulnerability from being exploited is to use proper input validation and output encoding before outputting user-supplied data. The plugin developers can patch the vulnerability by sanitizing the 'id' attribute value before using it in the HTML output. For example, the following modified code snippet utilizes the esc_attr() function provided by WordPress to escape the 'id' attribute value:

$result = '<div id="' . esc_attr( $a['id'] ) . '">' . do_shortcode('[notcaptcha]') . '</div>';

Original References

You can find more details about this vulnerability and the original disclosure in the following links:

- CVE-2025-23840 published on NVD
- Exploit-DB entry for CVE-2025-23840

Conclusion

By understanding the implications of the CVE-2025-23840 vulnerability and how it affects the Webjema WP-NOTCAPTCHA plugin, website developers can take appropriate action to secure their sites. Ensuring that proper input validation and output encoding is used throughout the application can help prevent similar vulnerabilities from occurring in the future.

Timeline

Published on: 02/17/2025 12:15:27 UTC