Executive brief
The Single Mailchimp plugin for WordPress, which allows site owners to integrate Mailchimp signup forms, contains a security flaw that allows users with contributor-level access or higher to inject malicious scripts into website pages. These scripts will automatically run in the browser of any visitor who views the affected page. This could lead to unauthorized actions being performed on behalf of site administrators or the theft of sensitive session information.
Technical details
The Single Mailchimp plugin for WordPress is vulnerable to Stored Cross-Site Scripting (XSS) due to insufficient input sanitization and output escaping within the 'single-mailchimp' shortcode. Specifically, the single_mailchimp() function in shortcodes.php fails to properly handle attributes such as autocomplete, label, placeholder, btn_text, success_msg, and error_msg, concatenating them directly into the HTML output. An authenticated attacker with contributor-level permissions or higher can exploit this by embedding malicious scripts into a post or page using the shortcode. These scripts execute in the context of any user's browser session when they visit the compromised page. The vulnerability affects all versions up to and including 1.4.
Affected products
- Single Mailchimp Single Mailchimp Up to, and including, 1.4
Timeline
- 2026-05-27: disclosed: Vulnerability published to the CVE list.
- 2026-05-27: advisory: Wordfence published the vulnerability details.