Executive Summary

The Single Mailchimp plugin for WordPress has a Stored Cross-Site Scripting (XSS) vulnerability in all versions up to and including 1.4. This occurs because the plugin does not properly sanitize or escape user-supplied shortcode attributes such as autocomplete, label, placeholder, btn_text, success_msg, and error_msg. These attributes are directly concatenated into the HTML output by the single_mailchimp() function, allowing an authenticated attacker with contributor-level access or higher to inject malicious scripts. These scripts execute whenever a user visits the affected page.

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Impact Analysis

This vulnerability can allow an attacker with contributor-level access to inject arbitrary malicious scripts into pages on your WordPress site. When other users visit these pages, the injected scripts will execute in their browsers. This can lead to theft of user credentials, session hijacking, defacement of the website, or distribution of malware, compromising the security and integrity of your site and its users.

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Mitigation Strategies

The vulnerability affects all versions of the Single Mailchimp plugin for WordPress up to and including 1.4. To mitigate this vulnerability, you should update the plugin to a version later than 1.4 where the issue is fixed.

Additionally, restrict contributor-level and higher access to trusted users only, as the vulnerability requires authenticated users with contributor-level access or above to exploit.

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