The present paper aims to compare and analyze the security of the most common three open-source Web Content Management Systems: WordPress, Joomla! and Drupal. The paper is focused on describing the main vulnerabilities regarding the security of CMS platforms and reflects relevant data that can be used to avoid the most common attacks. In the digital era, where all the information is stored on web servers to be accessed from everyone, security and confidential data protection is an important part when it comes to choosing  the right CMS for our needs.