A critical remote code execution vulnerability in PHPMailer, one of the most widely used PHP email sending libraries, could put millions of websites at risk of hacking.
The flaw was found by a security researcher named Dawid Golunski and an initial fix was included in PHPMailer 5.2.18, which was released Saturday. However, it turns out that the patch was incomplete and can be bypassed.
The PHPMailer library is used directly or indirectly by many content management systems (CMSs) including WordPress, Joomla and Drupal. Where the library is not included in their core code, it is likely available as a separate module or can be bundled with third-party add-ons.