The Anti-Spam by CleanTalk – Spam Protection Without CAPTCHA plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'useremail' parameter in all versions up to, and including, 6.89.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. Successful exploitation requires user registration to be open on the site, and script execution is triggered when an Administrator subsequently runs the plugin's user-spam scan and views the resulting Non-checkable users or Spam users tab — the plugin's own documented workflow.

The Anti-Spam by CleanTalk – Spam Protection Without CAPTCHA plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'comment' parameter in all versions up to, and including, 6.88 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This vulnerability is exploitable once a comment from the attacker's email address has been approved; on default WordPress installations, only the first comment from a given email address is held for moderation, meaning subsequent comments auto-approve and immediately expose the payload to site visitors.

Improper Neutralization of Input During Web Page Generation ("Cross-site Scripting") vulnerability in Drupal Anti-Spam by CleanTalk allows Reflected XSS. This issue affects Anti-Spam by CleanTalk versions: from 0.0.0 to 9.7.1.

The Anti-Spam by CleanTalk. Spam protection WordPress plugin before 6.79 does not properly sanitize content within a custom shortcode used in its email-encoding feature, allowing unauthenticated attackers to inject arbitrary web scripts into approved comments that will execute when any user (including administrators) views the post.

The Spam protection, Anti-Spam, FireWall by CleanTalk plugin for WordPress is vulnerable to unauthorized Arbitrary Plugin Installation due to an authorization bypass via reverse DNS (PTR record) spoofing on the 'checkWithoutToken' function in all versions up to, and including, 6.71. This makes it possible for unauthenticated attackers to install and activate arbitrary plugins which can be leveraged to achieve remote code execution if another vulnerable plugin is installed and activated. Note: This is only exploitable on sites with an invalid API key.